C Program To Reverse A Given String

The program to reverse a given string takes the input string and output reverse of the string. Each of the characters from the input string is extracted one at a time to achieve this task.

The program is compiled using Dev-C++ compiler version 4.9.9.2 installed on a Windows 7 64-bit system. However, you can use any other standard C compiler to run this program. To get an error-free program change the source code according to your compiler specifications.

You must be familiar with following C programming concepts to understand this program.

• C Reading Input Values
• C Data Types
• C Arrays
• C While Loop
• C Functions

Problem Definition

The program takes an input string at run-time using the builtin function gets (str) where str is a character array. In this array of characters, the beginning characters are exchanged with the ending characters of the string with the help of a temp variable.

For example

If the string is “ELEPHANT”. The letter is ‘E’ and ‘T’ are exchanged until all characters are reversed. The final output is TNAHPELE.

Program Code Reverse a String

#include <string.h>
#include <stdio.h>
#include <conio.h>
int main()
{
    char str[100],temp;
    int i,j=0;
    printf("\n Enter the String: ");
    gets(str);
    i=0;
    j = strlen(str)-1;
    while(i<j)
          {
        temp = str[i];
        str[i] = str[j];
        str[j] = temp;
        i++;
        j--;
    }
    printf("\n Reverse String is %s",str);
    getch();
}

Output

The output of the above program is given below. When the program ask for a string input, the user enters – MATHEMATICS. The program reverses the string and give following output.

Enter the String: MATHEMATICS
Reverse String is SCITAMEHTAM