C Program to Search and Replace Word with Specific Word

This is a C Program to search a word & replace it with the specified word.

Problem Description

This C Program Searches a Word & Replace it with the Specified Word.

Problem Solution

Take input from the user and performs string operations as shown in the program below.

Program/Source Code

Here is source code of the C Program to find the possible subsets of the String. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

 * C Program to Search a Word & Replace it with the Specified Word
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/*Function to replace a string with another string*/
char *rep_str(const char *s, const char *old, const char *new1)
    char *ret;
    int i, count = 0;
    int newlen = strlen(new1);
    int oldlen = strlen(old);
    for (i = 0; s[i] != '\0'; i++)    
        if (strstr(&s[i], old) == &s[i]) 
            i += oldlen - 1;
    ret = (char *)malloc(i + count * (newlen - oldlen));
    if (ret == NULL)
    i = 0;
    while (*s)
        if (strstr(s, old) == s) //compare the substring with the newstring
            strcpy(&ret[i], new1);
            i += newlen; //adding newlength to the new string
            s += oldlen;//adding the same old length the old string
        ret[i++] = *s++;
    ret[i] = '\0';
    return ret;
int main(void)
    char mystr[100], c[10], d[10];
    printf("Enter a string along with characters to be rep_strd:\n");
    printf("Enter the character to be rep_strd:\n");
    scanf(" %s",c);
    printf("Enter the new character:\n");
    scanf(" %s",d);
    char *newstr = NULL;
    newstr = rep_str(mystr, c,d);
    printf("%s\n", newstr);
    return 0;
Program Explanation

In this C Program, we are reading a string along with characters to be replaced using ‘mystr’. The rep_str() function is used to replace a string with another string. If condition statement is used to compare the length of the new and old string values are equal.


Using ret variable allocate memory. If that memory is NULL then it will exit the function. If else condition statement, is used to compare the value of substring with the newstring. If the condition is true, then execute the statement by copying the new string to the ret[] variable.

Add the value of newlength to the new string and also add the same old length to the old string. Otherwise, if the condition is false, then execute the else condition statement assign the value of ‘s’ variable to ‘ret[]’ variable. Print the replaced word using printf statement.

Runtime Test Cases
$ cc string31.c
$ a.out
Enter a string along with characters to be rep_strd:
prrrogram C prrrogramming
Enter the character to be rep_strd:
Enter the new character:
prrrogram C prrrogramming
pmmmrogram C pmmmrogramming

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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