Basic Functions in C

Hi there I am writing a program that needs to use a function to iterate through an array and pick out the index number that has a capital M then return that index number, and only for the first occurrence of a capital M. if no capital M is found, then return a value of -1. here is what I have at the moment (I could be way out in left field with this as I am new to functions).

#include <stdio.h>

int findM (char string[], int numVals){
int i = 0;
int indexM;

for (i = 0; i < numVals; ++i){
if (string[i] == 'M'){
    indexM = string[i];
    break;
}
    else {
    indexM = -1;               
   }
  } 
    return indexM;
}

int main(void) {
   char userString [15] = "M as in Mancy";
   printf("%d",findM(userString, 15));
    return 0;
}

in this example, the intended result is 0, as the first element of this string is a capital M, however, my result is 77 when compiled and ran. Thanks for any help guys!