random(), randomize()
Built-in function random() is used to generate pseudo random integer.
Rule: IntegerVariable = random(n);
Function random() needs header file <stdlib.h>. Return value of the function is int. Function random() will generate a pseudo random integer between 0 and n-1 where n is an integer.
Usage of random()
#include<iostream.h>
#include<stdlib.h>
void main()
{
int n1=random(100);
int n2=random(200);
cout<<“n1=”<<n1<<“,n2=”<<n2;
}
Running of the program three times, produces following outputs:
n1=40,n2=20
n1=40,n2=20
n1=40,n2=20
Rule: randomize();
Function randomize() needs header file <stdlib.h>. Return value of the function is void and function has no parameter. Function randomize() is used with function random(), so that function random() will generate different random integer for every run.
Usage of randomize()
#include<iostream.h>
#include<stdlib.h>
void main()
{
randomize();
int n1=random(100);
int n2=random(200);
cout<<“n1=”<<n1<<“,n2=”<<n2;
}
Running the programs two times, produces following outputs:
n1=51,n2=129
n1=27,n2=182
Function random(100) will generate a random integer between 0 and 99. Function random(200) will generate a random integer between 0 and 199. Every time the program is run, it displays the same pair of output. If we want different pair of values at different run, then we need function randomize(). |
Function random() can generate only non-negative integer values. But kindly note:
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100+random(100) will generate random integer between 100 and 199
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-random(100) will generate random integer between 0 and -99
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random(100)/10.0 will generate random floating point value between 0 and 9.9
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char(65+random(26)) will generate random character between ‘A’ and ‘Z’
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char(97+random(26)) will generate random character between ‘a’ and ‘z’
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Program to generate 15 random negative integers:
#include<iostream.h>
#include<stdlib.h>
void main()
{
randomize();
for (int x=0; x<15; x++)
{
int num=-random(100);
cout<<num<<‘ ‘;
}
}
Running of the program produces following output:
-53 -24 -78 -97 -41 -42 -20 -73 -91 -67 -98 -37 -34 -55 -97
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Program to generate 15 random floating point values:
#include<iostream.h>
#include<stdlib.h>
void main()
{
randomize();
for (int x=0; x<15; x++)
{
int num=10+random(90);
double val=num/10.0;
cout<<val<<‘ ‘;
}
}
Running of the program produces following output:
8.3 3.7 3.3 3.4 4.6 7.9 5 5.6 5.9 7.9 8.7 7 5.3 2.2 7.6
Expression num=10+random(90) will store a random integer between 10 and 99 in the variable num. Expression val=num/10.0 will store a random floating point between 1.0 and 9.9 in the variable val. |
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Program to generate 20 random uppercase characters:
#include<iostream.h>
#include<stdlib.h>
void main()
{
randomize();
for (int x=0; x<20; x++)
{
char ch=char(65+random(26));
cout<<ch<<‘ ‘;
}
}
Running of the program produces following output:
Z P J M B R B Q B X H O C Y E K V Y J O
Expression 65+random(26) will generate random integer between 65 and 90 (ASCII codes of uppercase letters). Typecasting the expression into a char will generate random uppercase characters. |
Array
An array is special type of variable used to represent many values of the same data type under one name in the computer’s main storage (RAM). Till now the variable of the fundamental date type that we have used in our program, stores only one value. An example is given below:
double num=6.5;
cout<<num<<endl;
cin>>num;
cout<<num<<endl;
Variable num is created with initial value 6.5. Value stored in variable num is displayed. New value is inputted in variables num and it replaces the old value stored in the variable num. A variable of the fundamental type can store only one value at a time. |
Array Definition: Array is a collection of homogeneous data type, stored under one variable name and memory is allocated contiguously. Collection means many, homogeneous mean similar and contiguous mean a block of continuous memory location (no hole in within the block). Array name is the name of the entire block.
Just like variable of fundamental type, array variable has to be created. Creating an array variable is almost similar to creating a variable of fundamental type. Only difference is, array size has to be specified with square brackets ([]) after the array variable name. Creating an array variable is also known as declaring or defining an array.
Rule: DataType ArrayName[ArraySize];
DataType : DataType could be fundamental data type or derived data type
ArrayName : ArrayName is the array variable name. It is an identifier name.
ArraySize : ArraySize is used to specify number values to be stored under ArrayName. ArraySize has to be a positive integer constant or a positive integer expression involving only integer constants.
Examples of correct (syntactically correct) array declarations are given below:
int roll[10];
char name[20];
double marks[40];
double rates[30];
Or,
const MAX=20;
int roll[MAX/2];
char name[MAX];
double marks[2*MAX];
double rates[MAX+10];
Or,
#define MAX 20
int roll[MAX/2];
char name[MAX];
double marks[2*MAX];
double rates[MAX+10];
Array size is either:
|
Examples of incorrect (syntactically incorrect) array declarations are given below:
int max = 25, size;
cin>>size;
char s1[size], s2[max];
int c1[0], c2[];
double a1[-20], a2[25.5];
|
In the computer’s main storage an array is represented as contiguous block of memory. Suppose an array is created as:
double marks[10];
We can visualize the array marks[] may be represented in the computer’s main storage as shown in the figure given below:
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9 |
Each component of an array is called an element (cell) of an array. Since array name represents many values, C++ compiler assigns a reference number to every element of an array. The reference number is called an index (subscript) of an array. In C++, array index starts from zero (0). First element of the array is the 0th element of an array. Index of the last element of array is calculated as array size – 1. For example if array size is 10 then index of 10th element is 9. Array index is a non-negative integer starting from 0. Every element of an array is called subscripted variable. Every element of an array is treated as a variable. Examples are given below:
int roll[10];
char name[20];
double marks[40];
ü Array roll[] is an array of integers and therefore every element of array roll[] will be treated like an integer type variable.
ü Array name[] is an array of characters and therefore every element of name[] will be treated like a character variable.
ü Array marks[] is array of floating point values and therefore every element of marks[] will be treated like a floating point variable.
After the creation of the array, we need to access elements of an array either to store value in elements of an array or to read value stored in elements of an array.
Rule to access an element of an array: ArrayName[Index]
double marks[5] → Array marks is createdmarks[0] → Represents the 1st element of marksmarks[1] → Represents the 2nd element of marksmarks[2] → Represents the 3rd element of marksmarks[3] → Represents the 4th element of marksmarks[4] → Represents the 5th element of marks |
Usage:
double marks[5];
marks[0]
marks[1]
marks[2]
marks[3]
marks[4]
There are several ways to store values in an array. One way to store values in the array is by using assignment operator. Values are to be assigned (stored) to every element of the array. An example is given below:
double marks[5];
marks[0]=76.5;
marks[1]=82.0;
marks[2]=69.5;
marks[3]=84.5;
marks[4]=59.0;
But generally values are stored in an array by inputting values from a keyboard. An example is given below:
double marks[5];
cout<<“Marks of Subject 1? “; cin>>marks[0];
cout<<“Marks of Subject 2? “; cin>>marks[1];
cout<<“Marks of Subject 3? “; cin>>marks[2];
cout<<“Marks of Subject 4? “; cin>>marks[3];
cout<<“Marks of Subject 5? “; cin>>marks[4];
Above method of inputting values in an array is only suitable when numbers of elements in array are relatively less. But more elegant way of inputting values in any array will be by using a loop. An example is given below:
double marks[5];
for (int k=0; k<5; k++)
{
cout<<“Marks of Subject “<<(k+1)<<“? “;
cin>>marks[k];
}
Incorrect way of inputting values in an array:
cin>>arrayname will flag syntax error in most arrays (syntax error will not be flagged if arrayname is an array of char). |
double marks[5];
cout<<“Input Marks? “;
cin>>marks;
Values stored in elements of an array can be displayed by using cout. An example is given below:
double marks[5];
for (int k=0; k<5; k++)
{
cout<<“Marks of Subject “<<(k+1)<<“? “; cin>>marks[k];
}
cout<<“Marks of Subject 1=”<<marks[0]<<endl;
cout<<“Marks of Subject 2=”<<marks[1]<<endl;
cout<<“Marks of Subject 3=”<<marks[2]<<endl;
cout<<“Marks of Subject 4=”<<marks[3]<<endl;
cout<<“Marks of Subject 5=”<<marks[4]<<endl;
Again this way of displaying an array is suitable if the array size is small. But a smart way of displaying values stored in an array is by using a loop. A complete program is given below showing inputting values in an array and displaying values stored in an array by using a loop:
#include<iostream.h>void main(){double a[10];for(int x=0; x<10; x++){cout<<“Value? “;cin>>a[x];}for(int k=0; k<10; k++)cout<<a[k]<<endl;} |
#include<iostream.h>const MAX=10;void main(){int a[MAX];for(int x=0; x<MAX; x++){cout<<“Value? “; cin>>a[x];}for(int k=0; k<MAX; k++)cout<<a[k]<<endl;} |
Example is given below showing incorrect way of displaying an array on the screen.
double a[5];
for(int x=0; x<5; x++)
{
cout<<“Input value? “; cin>>a[x];
}
cout<<marks;
cout<<marks; (generally cout<<arrayname;) is a syntactically correct statement. But cout<<arrayname; will not display values stored in the array marks, instead it will display address of arrayname. Again this is true for most arrays. If the arrayname is an array of char, then cout<<arrayname; will display the content of the array (display the string on the screen). String and array of char will be discussed later.
Initializer
Initializer is another way to assign values to elements of an array. An initializer can only be used with an array, when the array is getting created. After the creation of an array we cannot use an initializer to assigns values to elements of an array. An example is given below:
double a[5]={11.1, 33.3, 77.7, 22.2, 55.5};
for(int x=0; x<5; x++)
cout<<a[x]<<endl;
Running of the program segment produces following output:
11.1
33.3
77.7
22.2
55.5
In the above example, the number of values inside the initializer is equal to size of the array. The first value in the inside the initializer is assigned to the first element in the array, the second value inside the initializer is assigned to the second element in the array …, the last value inside the initializer is assigned to the last element in the array.
Bur what happens when values inside the initializer are either less or more than size of the array?
If the values inside the initializer are less than the size of the array, then the remaining elements of the array will be assigned the value 0 (zero).
double arr[5]={11.1, 33.3, 22.2};
for(int x=0; x<5; x++)
cout<<ar[x]<< endl;
Running of the program segment produces following output:
11.1
33.3
22.2
0
0
Remaining two elements of array arr[], arr[3] and arr[4] are assigned the value 0 (zero). An initializer must contain at least one value. Statement given below will flag error:
int arr[10]={};
If the values inside the initializer are more than the size of the array, then the compiler will flag syntax error. An example is given below:
double arr[5]={1.1, 3.3, 2.2, 5.5, 4.4, 6.6};
Array size is 5 but number of values inside the initializer is 6, compiler will flag syntax error. When an array is assigned values using an initializer, array size may be omitted from array declaration (definition). In that case number of values inside the initializer decides the size of the array. Array without a size is called open array. Some examples are given below:
int arr1[]={33.3, 22.2, 55.5, 44.4, 77.7, 66.6, 99.9, 88.8};
double arr2[]={30, 20, 50, 40, 60};
Array arr1[] will be created with size 8 since inside the initializer there are 8 values. Array arr2[] will be created with size 5 since inside the initializer there are 5 values.
Built-in functions random() and randomize() can be used to assign random values to elements of an array. Some examples are given below:
//Array of random integers#include<iostream.h>#include<stdlib.h>void main(){int a[10];randomize();for(int x=0; x<10; x++)a[x]=random(100);for(int k=0; k<10; k++)cout<<a[k]<<endl;} |
//Array of random integers#include<iostream.h>#include<stdlib.h>const MAX=10;void main(){int a[MAX];randomize();for(int x=0; x<MAX; x++)a[x]=random(100);for(int k=0; k<MAX; k++)cout<<a[k]<<endl;} |
//Array of random double values#include<iostream.h>#include<stdlib.h>const MAX=20;void main(){double a[MAX];randomize();for(int x=0; x<MAX; x++)a[x]=random(1000)/10.0;for(int k=0; k<MAX; k++)cout<<a[k]<<endl;} |
//Array of random characters#include<iostream.h>#include<stdlib.h>const MAX=40;void main(){char a[MAX];randomize();for(int x=0; x<MAX; x++)a[x]=char(97+random(26));for(int k=0; k<MAX; k++)cout<<a[k];} |
Array as Global variable and array as Local variable
An array created just after the header file and before any function block is called a Global array. A Global array can be used throughout the program and in every block of the program. An array created in block is called a Local array. A Local array can be used inside the block in which it was created and blocks nested below. Inside a block, if a Local array and a Global array have same name, then scope resolution operator (::) is to be used with the Global array name, so that Global array and Local array can be used inside the block. An example of Global array and Local array is given below:
#include<iostream.h>#include<stdlib.h>int ga[10];void arrfn(){int la1[10];for (int x=0; x<10; x++){ga[x]=random(100);la1[x]=random(100);}for (int k=0; k<10; k++)cout<<ga[k]<<la1[k]<<endl;}void main(){int la2[10];randomize();for (int x=0; x<10; x++){ga[x]=random(200);la2[x]=random(200);}for (int k=0; k<10; k++)cout<<ga[k]<<la2[k]<<endl;} |
#include<iostream.h>#include<stdlib.h>double ga[10];void arrfn(){double la1[10];for (int x=0; x<10; x++){ga[x]=random(100)/10.0la1[x]=random(100)/10.0;}for (int k=0; k<10; k++)cout<<ga[k]<<la1[k]<<endl;}void main(){double la2[10];randomize();for (int x=0; x<10; x++){ga[x]=random(200)/5.0;la2[x]=random(200)/5.0;}for (int k=0; k<10; k++)cout<<ga[k]<<la2[k]<<endl;} |
Array ga[] is Global array it can be used throughout the program, that is, array ga[] can be used in the main() function and in the function arrfn(). Arrays la1[] and la2[] are Local arrays. Array la1[] is local to function arrfn() and array la2[] is local to main() function.
Array as parameter to a user defined function
Just like any other data type, array type can be passed as parameter to a function. There are several ways of passing an array as parameter to a function. Array is always passed by reference to a function. The simplest way to pass an array as a parameter to function is to pass the array name as a parameter to the function. Function invocation will have function name and array name as parameter. Function header will have array name and the data type of the array as a parameter. Examples are given below to illustrate the concept:
| const MAX=20;void input(int a[]){for(int x=0; x<MAX; x++)a[x]=random(100);}Or,
void input(int a[]) { for(int x=0; x<MAX; x++) { cout<<“Value? “;cin>>a[x]; } } void main() { int arr[MAX]; randomize(); input(arr); for(int k=0; k<MAX; k++) cout<<arr[k]<<endl; } |
const MAX=20;void input(double a[]){for(int x=0; x<MAX; x++)a[x]=random(200)/5.0;}Or,
void input(double a[]) { for(int x=0; x<MAX; x++) { cout<<“Value?”;cin>>a[x]; } } void main() { double arr[MAX]; randomize(); input(arr); for(int k=0; k<MAX; k++) cout<<arr[k]<<endl; } |
| void input(int a[]){for(int x=0; x<20; x++)a[x]=random(100);}Or,void input(int a[])
{ for(int x=0; x<MAX; x++) { cout<<“Value?”;cin>>a[x]; } } void main() { int a1[20], a2[20]; randomize(); input(a1); input(a2); for(int k=0; k<20; k++) cout<<a1[k]<<a2[k]<<endl; } |
void input(double a[]){for(int x=0; x<20; x++)a[x]=random(200)/5.0;}Or,void input(double a[])
{ for(int x=0; x<20; x++) { cout<<“Value?”;cin>>a[x]; } } void main() { double a1[20], a2[20]; randomize(); input(a1); input(a2); for(int k=0; k<20; k++) cout<<a1[k]<<a2[k]<<endl; } |
Function input() is used to store values in the array a[] (a[] is the formal parameter) by either using random() or taking input from keyboard. Function definition of input() has only one formal parameter – array name (a[]) and data type of the array (int / double). An open array (a[]) is used to represent array as formal parameter. Size of the array is either user defined constant MAX or integer constant 20. When invoking function input() actual parameter is array name (arr – is the actual parameter). This way passing array name as a parameter to a function is suitable when the program deals with either one single array (array arr[] in the first example) or many arrays having same size (array a1[]and a2[] in the second example).
But when the program has to deal with many arrays of different sizes then we have a problem because in the user defined function we cannot use a constant as an array size. In such cases user defined function needs two parameters – array name (with data type) and size of the array (number elements in the array). Function header will have two parameters – array name (and data type of the array) and number of elements (integer type). Invocation of function will have two actual parameters – array name and number elements in the array. Some examples are given below:
| const MAX=20;void input(int a[], int n){for(int x=0; x<n; x++)a[x]=random(100);}Or,
void input(int a[], int n) { for(int x=0; x<MAX; x++) { cout<<“Value?”;cin>>a[x]; } } void display(int a[], int n) { for(int x=0; x<n; x++) cout<<a[x]<<‘ ‘; cout<<endl; } void main() { int arr1[MAX], arr2[30]; randomize(); input(arr1, MAX); input(arr2, 30); display(arr1, MAX); display(arr2, 30); } |
const MAX=20;void input(double a[], int n){for(int x=0; x<n; x++)a[x]=random(200)/5.0;}Or,
void input(double a[], int n) { for(int x=0; x<MAX; x++) { cout<<“Value?”;cin>>a[x]; } } void display(double a[], int n) { for(int x=0; x<n; x++) cout<<a[x]<<‘ ‘; cout<<endl; } void main() { double arr1[MAX], arr2[30]; randomize(); input(arr1, MAX); input(arr2, 30); display(arr1, MAX); display(arr2, 30); } |
User defined functions input() and display() have two formal parameters – array name (int / double a[]) and number of elements in the array (int n). Invocation of user defined functions input() and display() also have two actual parameters – array name (arr1 / arr2) and number of elements in the array (MAX / 30). This is the best way of passing array as parameter to a function since function can accept arrays of different sizes.
Program to find sum and average of values stored in an array.
#include<iostream.h>#include<stdlib.h>const MAX=20;void sumavg(int ar[], int n){int s=0;for(int k=0; k<n; k++)s+=ar[k];double av=s/double(n);cout<<“Sum=”<<s<<endl;cout<<“Average=”<<av<<endl;}void main(){int arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=random(1000);sumavg(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
#include<iostream.h>#include<stdlib.h>const MAX=20;void sumavg(double ar[], int n){double s=0;for(int k=0; k<n; k++)s+=ar[k];double av=s/n;cout<<“Sum=”<<s<<endl;cout<<“Average=”<<av<<endl;}void main(){double arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=random(2000)/5.0;sumavg(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
Program to find GM and HM of values stored in an array.
#include<iostream.h>#include<stdlib.h>#include<math.h>const MAX=20;void gmhm(int ar[], int n){double s=0, p=1;for(int k=0; k<n; k++){p*=ar[k]; s+=1.0/ar[k]}double gm=pow(p, 1.0/n);double hm=n/s;cout<<“GM=”<<gm<<endl;cout<<“HM=”<<hm<<endl;}void main(){int arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=100+random(900);gmhm(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
#include<iostream.h>#include<stdlib.h>#include<math.h>const MAX=20;void gmhm(double ar[], int n){double s=0, p=1;for(int k=0; k<n; k++){p*=ar[k]; s+=1/ar[k]}double gm=pow(p, 1.0/n);double hm=n/s;cout<<“GM=”<<gm<<endl;cout<<“HM=”<<hm<<endl;}void main(){double arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=(10+random(90))/5.0;gmhm(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
Program to find maximum and minimum values stored in an array.
#include<iostream.h>#include<stdlib.h>void maxmin(int ar[], int n){int hi=ar[0], lo=ar[0];for(int k=0; k<n; k++)if (ar[k]<lo)lo=ar[k];for(int x=0; x<n; x++)if (ar[x]>hi)hi=ar[x];cout<<“Min=”<<lo<<endl;cout<<“Max=”<<hi<<endl;}void main(){int arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=100+random(900);maxmin(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
#include<iostream.h>#include<stdlib.h>void maxmin(double ar[], int n){double hi=ar[0], lo=ar[0];for(int k=0; k<n; k++)if (ar[k]<lo)lo=ar[k];for(int x=0; x<n; x++)if (ar[x]>hi)hi=ar[x];cout<<“Min=”<<lo<<endl;cout<<“Max=”<<hi<<endl;}void main(){double arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=(10+random(90))/5.0;maxmin(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
Program to find minimum value stored in an array and its position in the array.
#include<iostream.h>#include<stdlib.h>void arrmin(int ar[], int n){int lo=ar[0];int pos=0;for(int k=0; k<n; k++)if (ar[k]<lo){lo=ar[k]; pos=k;}cout<<“Min=”<<lo<<endl;cout<<“Position=”<<pos<<endl;}void main(){int arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=100+random(900);arrmin(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
#include<iostream.h>#include<stdlib.h>void arrmin(double ar[], int n){double lo=ar[0];int pos=0;for(int k=0; k<n; k++)if (ar[k]<lo){lo=ar[k]; pos=k;}cout<<“Min=”<<lo<<endl;cout<<“Position=”<<pos<<endl;}void main(){double arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=(10+random(90))/5.0;arrmin(arr, MAX);for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
Program to reverse elements of an array
#include<iostream.h>#include<stdlib.h>void reverse(int ar[], int n){int ri=n-1;for(int le=0; le<ri; le++){int t=ar[le];ar[le]=ar[ri];ar[ri]=t;ri–;}}void main(){int arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=100+random(900);cout<<“Before reversing\n”;for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;reverse(arr, MAX);cout<<“After reversing\n”;for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
#include<iostream.h>#include<stdlib.h>void reverse(double ar[], int n){int ri=n-1;for(int le=0; le<ri; le++){double t=ar[le];ar[le]=ar[ri];ar[ri]=t;ri–;}}void main(){double arr[MAX];randomize();for(int x=0; x<MAX; x++)arr[x]=random(2000)/5.0;cout<<“Before reversing\n”;for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;reverse(arr, MAX);cout<<“After reversing\n”;for(int k=0; k<MAX; k++)cout<<arr[k]<<endl;} |
String Variable – Array of Characters
String constant is a sequence of characters enclosed within a pair of double quotes (“). To store a string in computer’s main memory we need a string variable. In C++ an array of characters is generally called a string variable. But every array of characters is not a string variable. A string variable is an array of characters terminated by a Nul character (”). ASCII code of Nul character is 0 (zero). Normally creating a string variable simply means creating an array of characters. Examples are given below:
| Arrays name and address are string variables. But they are not a string variable since terminating Nul character is missing from the arrays. |
char name[20];
char address[80];
const MAX=20;
char name[MAX];
char address[4*MAX];
Initializer: An initializer can be used to assign a value to a string. Initializer is used with a string variable to assign value when string variable is being created. If number of characters inside the initializer is less than the array size, then the remaining elements of the string variable are assigned Nul character. If number of characters inside initializer is more than the size of the array, then compiler will flag error. Examples are given below:
char str1[10]={‘A’, ‘H’, ‘M’, ‘A’, ‘D’, ‘I’};
char str2[10]=”AHMADI”;
char str3[]={‘A’, ‘H’, ‘M’, ‘A’, ‘D’, ‘I’, ”};
char str4[]=”AHMADI”;
Strings str1 and str2 will store “AHMADI” in computer’s main storage in the following way:
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5 |
6 |
7 |
8 |
9 |
A |
H |
M |
A |
D |
I |
All elements after ‘I’ will have Nul character. String st1 is initialized using an initializer but string str2 is initialized by assigning a string constant. Assigning a string constant to initialize a string is always preferred method as compared to using an initializer. Strings str3 and str4 will store “AHMADI” in computer’s main storage in the following way:
0 |
1 |
2 |
3 |
4 |
5 |
6 |
A |
H |
M |
A |
D |
I |
After ‘I’ (5th character) there will be terminating Nul character (6th character). Size of strings str3 will be 6 since there are 6 characters inside the initializer. Size of string str4 will be 6 as well even though string constant “AHMADI” has only 5 characters. This is because one more extra element is needed to store the terminating Nul character.
String Input: Input from the keyboard is the most common way of storing value in a string variable. As mentioned earlier cin>>ArrayName; where ArrayName is not an array of char, will be flagged as syntax error. But if ArrayName is an array of char then it is possible to input a string from a keyboard. An example is given below:
char name[15];
cout<<“Input name? “; cin>>name;
Running of the above program segment produces screen like:
Input name? ARINDAM◄─┘
String constant “ARINDAM” get stored in the string variable name in computer’s main storage in the following way:
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
A |
R |
I |
N |
D |
A |
M |
? |
? |
? |
? |
? |
? |
? |
First 7 (seven) elements of string variable name will contain “ARINDAM” and there will be a terminating Nul character after ‘M’. Remaining elements of string variable name will contain garbage character (‘?’ represent garbage character).
char name[15];
cout<<“Input name? “; cin>>name;
Running of the above program segment produces screen like:
Input name? ARINDAM GUPTA◄─┘
But string constant “ARINDAM” only get stored in the string variable name. This is because cin treats space as a separator. So according to cin, “ARINDAM” and “GUPTA” are two pieces of data. Therefore it is not possible to input a string containing space using cin. If we want to input a string containing space then we have to use function gets() from the header file <stdio.h>.
Rule for using gets():
gets(StringVar);
Usage:
char name[15];
cout<<“Input name? “; gets(name);
Running of the above program segment produces screen like:
Input name? ARINDAM GUPTA◄─┘
String constant “ARINDAM GUPTA” will be stored in the string variable name in computer’s main storage in the following way:
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
A |
R |
I |
N |
D |
A |
M |
G |
U |
P |
T |
A |
? |
First 13 (thirteen) characters of string variable name will contain string constant “ARINDAM GUPTA”. 14th character will be a terminating Nul character. Function gets() can be used to input a string without space as well.
String Copy: Assignment operator (=) is used to copy value to a variable of fundamental type. Assigning value to a variable can be interpreted as copying value to a variable. Assignment operator cannot be used to copy a string. To copy a string we need a function strcpy(). Function strcpy() requires header file <string.h>. Example of strcpy() is given below:
char song[15];
strcpy(song, “NOVEMBER RAIN”);
cout<<song;
char name[15]=”NOVEMBER RAIN”, song[15];
strcpy(song, name);
cout<<song;
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
N |
O |
V |
E |
M |
B |
E |
R |
R |
A |
I |
N |
? |
Function strcpy() will copy string constant “NOVEMBER RAIN” into a string variable song and Nul character will be appended after ‘N’ (13th character of the string variable song) .
String Display
As discussed earlier, a loop is used to display values stored in an array. Also we mentioned ealier that cout<<ArrayName; if ArrayName, where ArrayName is not an array of char, will display address of ArrayName. But if ArrayName is an array of char then it will display string value stored in the ArrayName. Function puts() also displays a string and it requires header file <stdio.h>. There is no added advantage of using puts() to display a string as compared to cout. When a string is displayed using cout (puts()), cout (puts()) assumes that the string terminated by a Nul character. An example is given below:
char song[15], str[4]=”ABCD”;
cout<<“Song Name? “; gets(song);
cout<<“Song Name: “<<song<<endl;
cout<<“Song Name: “;
puts(song);
puts(str);
Running of the program segment produces following screen
Song Name? NOVEMBER RAIN
Song Name: NOVEMBER RAIN
Song Name: NOVEMBER RAIN
ABCD╕~↕
Last puts(str) displays ABCD╕~↕ since string variable str has 4 elements, initializer has 4 characters, hence no room for the terminating Nul character. So puts(str) displays ABCD, four characters of the string then look for terminating Nul character. But puts() could not find Nul character after D and therefore displays few garbage characters (╕~↕), till it finds the Nul character. There are two minor differences between cout and puts().
cout |
puts() |
|
|
|
|
Important string functions are given below:
Function Name |
Header File |
Usage |
gets(s) |
stdio.h |
Input string s from keyboard, with or without space |
puts(s) |
stdio.h |
Displays string s on the screen, assumes that string is terminated by Nul character |
strlen(s) |
string.h |
Counts number of characters in string s excluding Nul character. |
strcpy(s1,s2) |
string.h |
String s2 is copied to string s1 |
strupr(s) |
string.h |
Converts string s into uppercase |
strlwr(s) |
string.h |
Converts string s into lowercase |
strrev(s) |
string.h |
Reverses a string s, string DOWN becomes NWOD |
strcat(s1,s2) |
string.h |
Appends (concatenate) string s2 after string s1. |
strcmp(s1,s2) |
string.h |
Compares 2 strings s1 and s2 lexically using ASCII code |
stricmp(s1,s2)strcmpi(s1,s2) |
string.h |
Compares 2 strings s1 and s2 lexically using ASCII code but ignoring case |
Keyword typedef
Keyword typedef is used create a user defined data type. Use of keyword typedef is explained with examples given below:
| //Without typedefint mark[5];char name[20]cout<<“Name?”;gets(name);for (int x=0; x<5; x++){
cout<<“Mark?”; cin>>mark[x]; } |
//With typedeftypedef int marklist[5];typedef char string[20];marklist mark;string name;cout<<“Name?”; gets(name);for (int x=0; x<5; x++)
{ cout<<“Mark?”; cin>>mark[x]; } |
Statement typedef int marklist[5]; creates a data type called marklist which is an array of integers. Statement typedef char string[20]; creates a data type called string which is an array of characters. A variable mark (an array of integer) is created of the type marklist and a variable name (an array of character) is created of the type string. Data type marklist and name are the user defined data type created by keyword typedef.
C++ array (array of string) functions (sort, search, merge, insert & delete):
typedef char string[20];
void bubblesort(string arr[], int n)
{
for (int x=1; x<n; x++)
for (int k=0; k<n-x; k++)
if (strcmp(arr[k], arr[k+1])>0)
{
string t;
strcpy(t, arr[k]);
strcpy(arr[k], arr[k+1]);
strcpy(arr[k+1], t);
}
}
void selectionsort(string arr[], int n)
{
for (int x=0; x<n-1; x++)
{
string min;
strcpy(min,arr[x]);
int pos=x;
for (int k=x+1; k<n; k++)
if (strcmp(min, arr[k])>0)
{
strcpy(min, arr[k]);
pos=k;
}
strcpy(arr[pos], arr[x]);
strcpy(arr[x], min);
}
}
void insertionsort(string arr[], int n)
{
for (int x=1; x<n; x++)
{
string t;
strcpy(t,arr[x]);
int k=x-1;
while (k>=0 && strcmp(t, arr[k])<0)
{
strcpy(arr[k+1], arr[k]);
k–;
}
strcpy(arr[k+1], t);
}
}
int binarysearch(string arr[], int n, string item)
{
int lb=0, ub=n-1, mid, found=0;
while (lb<=ub && found==0)
{
mid=(lb+ub)/2;
if (strcmp(item, arr[mid])<0)
ub=mid-1;
else
if (strcmp(item, arr[mid])>0)
lb=mid+1;
else
found=1;
}
return found;
}
Or,
void binarysearch(string arr[], int n, string item)
{
int lb=0, ub=n-1, mid, found=0;
while (lb<=ub && found==0)
{
mid=(lb+ub)/2;
if (strcmp(item, arr[mid])<0)
ub=mid-1;
else
if (strcmp(item, arr[mid])>0)
lb=mid+1;
else
found=1;
}
if (found==1)
cout<<item<<” found in the array\n”;
else
cout<<item<<” not found in the array\n”;
}
Or,
void binarysearch(string arr[], int n)
{
int lb=0, ub=n-1, mid, found=0;
string item;
cout<<“Item to search? “; gets(item);
while (lb<=ub && found==0)
{
mid=(lb+ub)/2;
if (strcmp(item, arr[mid])<0)
ub=mid-1;
else
if (strcmp(item, arr[mid])>0)
lb=mid+1;
else
found=1;
}
if (found==1)
cout<<item<<” found in the array\n”;
else
cout<<item<<” not found in the array\n”;
}
int linearsearch(string arr[], int n, string item)
{
int k=0, found=0;
while (k<n && found==0)
if (strcmp(item, arr[k])==0)
found=1;
else
k++;
return found;
}
Or,
void linearsearch(string arr[], int n, string item)
{
int k=0, found=0;
while (k<n && found==0)
if (strcmp(item, arr[k])==0)
found=1;
else
k++;
if (found==1)
cout<<item<<” found in the array\n”;
else
cout<<item<<” not found in the array\n”;
}
Or,
void linearsearch(string arr[], int n)
{
int k=0, found=0;
string item;
cout<<“Item to search? “; gets(item);
while (k<n && found==0)
if (strcmp(item, arr[k])==0)
found=1;
else
k++;
if (found==1)
cout<<item<<” found in the array\n”;
else
cout<<item<<” not found in the array\n”;
}
void merge(string a[], string b[], string c[], int n1, int n2)
{
int i=0, j=0, k=0;
while (i<n1 && j<n2)
if (strcmp(a[i], b[j])<0)
strcpy(c[k++], a[i++]);
else
strcpy(c[k++], b[j++]);
while (i<n1)
strcpy(c[k++], a[i++]);
while (j<n2)
strcpy(c[k++], b[j++]);
}
void arrayins(string arr[], int& n, int pos, string item)
{
if (n==MAX) //Size of array is MAX
cout<<“Overflow\n”;
else
{
for (int x=n-1; x>=pos; x–)
strcpy(arr[x+1], arr[x]);
strcpy(arr[pos], item);
n++;
cout<<item<<” inserted in the array\n”;
}
}
void arraydel(string arr[], int& n, int pos)
{
if (n==0)
cout<<“Underflow\n”;
else
{
cout<<arr[pos]<<” deleted from the array\n”;
for (int x=pos+1; x<n; x++)
strcpy(arr[x-1], arr[x]);
n–;
}
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