Notes

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

void replace(char*);

int main() {
char str[80]={};
printf("Enter a sentence: ");
gets(str);
replace(str);
printf("nNew sentence is: %s",str);
return 0;
}

void replace(char *str) {
char word1[20];
char word2[20];
char temp1[20]={};
char temp2[20]={};
char sentc1[80]={};
char sentc2[80]={};
char temp[80]={};
char *adres;
int i = 0, j;
for (;;) {
printf("nEnter the word you want to replace: ");
gets(word1);
sprintf(temp1," %s ",word1);
strcpy(word1,temp1);
adres = strstr(str, word1);
if (adres == NULL) {
printf("nError %s doesn't exist", word1);
continue;
}
printf("nEnter the new word: ");
gets(word2);
sprintf(temp2," %s ",word2);
strcpy(word2,temp2);
j = adres - str;
strncpy(sentc1,str,j);
for(j;j<strlen(str);j++){
sentc2[i]=str[j];
i++;
}
strcpy(temp,sentc2);
if(strlen(word1)-strlen(word2)!=0){
for(i=0;i<strlen(sentc2);i++){
sentc2[strlen(word2)+i]=temp[strlen(word1)+i];
}
for(i=0;i<strlen(word2);i++){
sentc2[i]=word2[i];
}
}
else{
for(i=0;i<strlen(word2);i++){
sentc2[i]=word2[i];
}
}
strcat(sentc1,sentc2);
strcpy(str,sentc1);
break;
}
}