C program to Reverse a String

How to write a C program to Reverse a String without using the strrev function with an example? To demonstrate this, we are going to use For Loop, While Loop, Functions, and Pointers.

C program to Reverse a String Example

This program allows the user to enter any character array. Next, it will use the For Loop to iterate each character and save the characters in inverse order.

#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str[100], RevStr[100];
  	int i, j, len;
 
  	printf("\n Please Enter any Text :  ");
  	gets(Str);
  	
  	j = 0;
  	len = strlen(Str);
 
  	for (i = len - 1; i >= 0; i--)
  	{
  		RevStr[j++] = Str[i];
  	}
  	RevStr[i] = '\0';
 
  	printf("\n And the Result of It is = %s", RevStr);
  	
  	return 0;
}

From the above C Programming screenshot, you can observe that,

str[] = Hello
j = 0
len = strlen(Str) = 5.

The strlen function is used to find the length of the input string. Let’s use that length in reverse a string programming flow. Please refer to the strrev function.

For Loop First Iteration: for (i = len – 1; i >= 0; i–)
=> for (i = 5 – 1; 4 >= 0; 4–)
The condition (4 >= 0) is True.
RevStr[j++] = Str[i]
RevStr[0] = Str[4] = 0

Second Iteration: for (i = 4 – 1; 3 >= 0; 3–)
The condition (3 >= 0) is True.
RevStr[1] = Str[3] = l

Third Iteration of a program: for (i = 3 – 1; 2 >= 0; 2–)
The condition (2 >= 0) is True.
RevStr[2] = Str[2] = l

Fourth Iteration: for (i = 2 – 1; 1 >= 0; 1–)
The condition (1 >= 0) is True.
RevStr[3] = Str[1] = e

Fifth Iteration: for (i = 1 – 1; 0 >= 0; 0–)
The condition (0 >= 0) is True.
RevStr[4] = Str[0] = H

Next, the condition inside the For Loop will fail

C Program to Reverse a String Example 2

Instead of storing the results in a separate array, we were directly printing the string characters in reverse order in this program.

#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str[100];
  	int i, ln;
 
  	printf("\n Before :  ");
  	gets(Str);
  	
  	ln = strln(Str);
  	
 	printf("\n After : "); 
  	for (i = ln - 1; i >= 0; i--)
  	{
  		printf("%c", Str[i]);
  	}

  	return 0;
}

 Before :  Tutorial Gateway

 After : yawetaG lairotuT

In this example, we are using the temp variable to change the location of the character. It is something like a program to reverse a string using the swapping technique.

/* using temp variable */
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str[100], temp;
  	int i, j, len;
 
  	printf("\n Actual :  ");
  	gets(Str);
  	
  	len = strlen(Str) - 1;
 
  	for (i = 0; i < strlen(Str)/2; i++)
  	{
  		temp = Str[i];
  		Str[i] = Str[len];
  		Str[len--] = temp;
  	}
 
  	printf("\n Result = %s", Str);
  	
  	return 0;
}

 Actual :  C Programming

 Result = gnimmargorP C

C program to Reverse a String Using Functions

This example is the same as above. However, this time we are using the recursive Functions to reverse the original and separate the logic from the main program.

#include <stdio.h>
#include <string.h>

void revText(char [], int, int);
 
int main()
{
  	char Str[100], temp;
  	int i, j, len;
 
  	printf("\n Please Enter :  ");
  	gets(Str);
  	
  	len = strlen(Str);
  	revText(Str, 0, len -1);
 
  	printf("\n After = %s", Str);
  	
  	return 0;
}

void revText(char Str[], int i, int len)
{
	char temp;
	temp = Str[i];
	Str[i] = Str[len - i];
	Str[len - i] = temp;
	
  	if (i == len/2)
  	{
		return;
  	}
  	revText(Str, i + 1, len);
}

 Please Enter :  Learn Programming

 After  = gnimmargorP nraeL

C program to Reverse a String Using Pointers

This program to reverse a string is the same as above, but this time we are using Pointers to separate the logic from the main function.

#include <stdio.h>
#include <string.h>

char* textRe(char *Str)
{
	static int i = 0;
	static char RevStr[10];
	
	if(*Str)
	{
		textRe(Str + 1);
		RevStr[i++] = *Str;
	}
	return RevStr;
}
 
int main()
{
  	char Str[100], temp;
  	int i, j, len;
 
  	printf("\n Enter  :  ");
  	gets(Str);
 
  	printf("\n Result = %s", textRe(Str));
  	
  	return 0;
}

 Enter :  Hello World!

 Result = !dlroW olleH