C program to Reverse a String

In this article, We will show you, How to write a C program to Reverse a String without using strrev function with example. To demonstrate the same we are going to use For Loop, While Loop, Functions, and Pointers.

C program to Reverse a String Example 1

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

/* C program to Reverse a String without using strrev() */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str[100], RevStr[100];
  	int i, j, len;
 
  	printf("\n Please Enter any String :  ");
  	gets(Str);
  	
  	j = 0;
  	len = strlen(Str);
 
  	for (i = len - 1; i >= 0; i--)
  	{
  		RevStr[j++] = Str[i];
  	}
  	RevStr[i] = '\0';
 
  	printf("\n String after Reversing = %s", RevStr);
  	
  	return 0;
}

OUTPUT

From the above screenshot you can observe that,
str[] = Hello
j = 0
len = strlen(Str) = 5.
The strlen is a string function used to find the string length.

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: 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 reverse string in separate array, in this program, we directly printing the characters in reverse order .

/* C program to Reverse a String without using strrev() */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str[100];
  	int i, len;
 
  	printf("\n Please Enter any String :  ");
  	gets(Str);
  	
  	len = strlen(Str);
  	
 	printf("\n String after Reversing : "); 
  	for (i = len - 1; i >= 0; i--)
  	{
  		printf("%c", Str[i]);
  	}

  	return 0;
}

OUTPUT

C program to Reverse a String Example 3

In this program we are using the temp variable to change the characters location. It is something like swapping technique.

/* C program to Reverse a String without using strrev() */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str[100], temp;
  	int i, j, len;
 
  	printf("\n Please Enter any String :  ");
  	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 String after Reversing = %s", Str);
  	
  	return 0;
}

OUTPUT

C program to Reverse a String Using Functions

This program is same as above but this time we are using recursive Functions concept to separate the logic from main program.

/* C program to Reverse a String without using strrev() */
 
#include <stdio.h>
#include <string.h>

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

void reverse_String(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;
  	}
  	reverse_String(Str, i + 1, len);
}

OUTPUT

C program to Reverse a String Using Pointers

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

/* C program to Reverse a String without using strrev() */
 
#include <stdio.h>
#include <string.h>

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

OUTPUT

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