C Program to Replace a Word in a Text By Another Given Word

// C program to search and replace 
// all occurrences of a word with 
// other word. 
#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 

// Function to replace a string with another 
// string 
char* replaceWord(const char* s, const char* oldW, 
                const char* newW) 
{ 
    char* result; 
    int i, cnt = 0; 
    int newWlen = strlen(newW); 
    int oldWlen = strlen(oldW); 

    // Counting the number of times old word 
    // occur in the string 
    for (i = 0; s[i] != '\0'; i++) { 
        if (strstr(&s[i], oldW) == &s[i]) { 
            cnt++; 

            // Jumping to index after the old word. 
            i += oldWlen - 1; 
        } 
    } 

    // Making new string of enough length 
    result = (char*)malloc(i + cnt * (newWlen - oldWlen) + 1); 

    i = 0; 
    while (*s) { 
        // compare the substring with the result 
        if (strstr(s, oldW) == s) { 
            strcpy(&result[i], newW); 
            i += newWlen; 
            s += oldWlen; 
        } 
        else
            result[i++] = *s++; 
    } 

    result[i] = '\0'; 
    return result; 
} 

// Driver Program 
int main() 
{ 
    char str[] = "xxforxx xx for xx"; 
    char c[] = "xx"; 
    char d[] = "Geeks"; 

    char* result = NULL; 

    // oldW string 
    printf("Old string: %s\n", str); 

    result = replaceWord(str, c, d); 
    printf("New String: %s\n", result); 

    free(result); 
    return 0; 
} 

// C Program to replace a word in a text by another given
// word by inplace updation
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void replaceWord(char* str, char* oldWord, char* newWord)
{
    char *pos, temp[1000];
    int index = 0;
    int owlen;

    owlen = strlen(oldWord);

    // Repeat This loop until all occurrences are replaced.

    while ((pos = strstr(str, oldWord)) != NULL) {
        // Bakup current line
        strcpy(temp, str);

        // Index of current found word
        index = pos - str;

        // Terminate str after word found index
        str[index] = '\0';

        // Concatenate str with new word
        strcat(str, newWord);

        // Concatenate str with remaining words after
        // oldword found index.
        strcat(str, temp + index + owlen);
    }
}

int main()
{
    char str[1000], oldWord[100], newWord[100];
    printf("Enter the string: ");
    gets(str);

    printf("Enter the word to be replaced: ");
    gets(oldWord);

    printf("Replace with: ");
    gets(newWord);

    replaceWord(str, oldWord, newWord);

    printf("\nModified string: %s", str);

    return 0;
}