Function takes in two strings, want to compare nth character

I have a f开发者_JAVA百科unction that takes in two strings, and I want to, let's say compare the 2nd letter of each string to the other. How do I fix this statement:

if (strncmp(str1 + 1, str2 + 1) != 0) {
...

I get an error stating that passing the argument makes a pointer from an integer without a cast.

if (str1[1] == str2[1]) {
    /* Do something */
}

If you want to allow the possibility that any of the strings can be smaller than the position you want to compare:

/* Return 1 if s1[n] > s2[n], 0 if s1[n] == s2[n], -1 if s1[n] < s2[n].
   Return -2 if any of the strings is smaller than n bytes long. */
int compare_nth(const char *s1, const char *s2, size_t n)
{
    size_t i;

    for (i=0; i < n; ++i)
        if (s1[i] == 0 || s2[i] == 0)
            return -2;

    if (s1[n] < s2[n])
        return -1;
    else if (s1[n] > s2[n])
        return 1;
    else
        return 0;
}

Then, to do something when the nth characters are equal, you can do:

if (compare_nth(s1, s2, n) == 0) {
    /* do whatever you want to do here */
}

If you know for sure that there are at least n characters in each of the strings, you can just do what others said:

if (s1[n] == s2[n]) {
    /* do whatever you want to do here */
}

(Note: since indexing in C is from 0, n is used in the same sense here. So, to test the second characters, n would be 1.)