Question

Given 2 strings, write a function that returns the position of String B that matches String A if String A is a substring of String B. Otherwise return -1.
Example:

strA = "ello"
strB = "Hello_World"
Your function should return 1.

strA = "blah"
strB = "blha"
Your function should return -1.

Answer 1

Brute force version:

int strpos(char* a, char* b) {
  int n1, n2, i, j;
  n1 = strlen(a);
  n2 = strlen(b);
  for (i = 0; i < n1-n2; i++) {
    for (j = 0; j < n2; j++) {
      if (a[i+j] != b[j]) break;
      else if (j+1 == n2) return i;
    }
  }
  return -1;
}

More effective algorithms: Wikipedia: String searching