Write a C program to reverse the string without using strrev() ?

This is simple logic which can reverse whole string without using library function strrev( ) or any other temporary string, we just use one temporary char variable. 

 

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

void main()
{
   char str[10],temp;
   int i,len;
   
   printf("Enter String : ");
   scanf("%s",str);
   
   len=strlen(str)-1;
   
   for(i=0;i<strlen(str)/2;i++)
   {
      temp=str[i];
      str[i]=str[len];
      str[len--]=temp;
   }
   printf("\nReverse string :%s",str);
   getch();
}

 

Probable errors : Here strlen( ) gives you the length of string without null character and we minus 1 from complete length because our for loop will start with 0(zero). If you do not minus length of string by 1 then your printf function will not print anything because you shift last null character on first position and string will end before start.

Reverse string using recursion

#include<stdio.h>

#define MAX 10		// Maximum size of string

/* Reverse the String using Recursion */
char* ReverseString(char *str)
{
    static int i=0;
    static char rev[MAX];

    if(*str)
	{
         ReverseString(str+1);
         rev[i++] = *str;		
    }

    return rev;		// Return index of array every time
}

/* Main method */
int main()
{
   	char str[MAX];
   	gets(str);
   
    printf (" %s \n", ReverseString(str));
         
	return 0;
}

 

Output

 

Suggested Reading

1. Write a C program to reverse the words in a sentence in place
2. Write your own trim() or squeeze() function to remove the spaces from a string
3. Write a C program which does wildcard pattern matching algorithm

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