Question

How to find the position of the first occurrence of a substring in a string with C

Answer 1

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

int find_substring(const char *mainString, const char *subString) {
    char *position = strstr(mainString, subString);
    if (position != NULL) {
        return position - mainString; // Calculate the index
    }
    
    return -1; // Indicating the substring was not found
}

int main() {
    char str[] = "I bought running shoes, but they started running alone, now we are both happy";
    char substring[] = "running";

    int position = find_substring(str, substring);

    if (position != -1) {
        printf("The first occurrence of \"%s\" is at position: %d\n", substring, position);
    } else {
        printf("Substring not found!\n");
    }

    return 0;
}


/*
run:

The first occurrence of "running" is at position: 9

*/

 

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Answer 2

#include <stdio.h>
#include <string.h>
 
int main() {
    char str[] = "I bought running shoes, but they started running alone, now we are both happy";
    char substring[] = "running";
 
    int position = (int)(strstr(str, substring) - str);
 
    if (position != -1) {
        printf("The first occurrence of \"%s\" is at position: %d\n", substring, position);
    } else {
        printf("Substring not found!\n");
    }
 
    return 0;
}
 
 
/*
run:
 
The first occurrence of "running" is at position: 9
 
*/

 

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