having some difficulty with some code around strncmp in C

having some difficulty with some code around strncmp in C just wondering if there is someone that ran into the same problem has me

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

int endsWith(char* longStr, char* shortStr);

int main()
{
    char* longString = "Grant is The man";
    char* shortString = "man";
    endsWith(longString,shortString);
    printf("%s\n",shortString);
}

int endsWith(char longStr, char shortStr)
{
    int offset;
    for (offset = 0 ; offset < strlen(shortStr) - strlen(longStr) ; offset ++)
        if (strncmp( longStr , shortStr + offset , strlen(longStr)) == 0)
            return 1;

    return -1;
}

the return should be man and if i inserted is the nothing should be returned or 0.

There are a number of problems with your code.

• your declaration of endsWith() does not match its definition.

• main() is ignoring the return value of endsWith()

• there is no need for a loop in endsWith() at all. Your approach is implementing an indexOf() function rather than an endsWith() function. You can calculate the needed offset with a single subtraction, no looping required.

  But, even if a loop were needed, you are not calculating the loop condition correctly. You are subtracting a larger value from a shorter value, which will result in a negative value. But since strlen() returns an unsigned type, a negative will wrap to a very large positive value, so you end up looping more than you need.

• you are passing the wrong parameters to strncmp(). Since you want to compare the end of the longStr to see if it matches the shortStr, you need to pass longStr + offset instead of shortStr + offset, and also pass strlen(shortStr) instead of strlen(longStr).

• endsWith() should return 0 if a match is not found, not -1.

With that said, try something more like this instead:

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

int endsWith(const char* longStr, const char* shortStr);

int main()
{
    const char* longString = "Grant is The man";
    const char* shortString = "man";
    if (endsWith(longString, shortString))
        printf("Ends with %s\n", shortString);
    else
        printf("Does not end with %s\n", shortString);
}

int endsWith(const char* longStr, const char* shortStr)
{
    size_t longLen = strlen(longStr);
    size_t shortLen = strlen(shortStr);
    return (
        (longLen >= shortLen) &&
        (strncmp(longStr + (longLen-shortLen), shortStr, shortLen) == 0)
        ) ? 1 : 0;
}