How to do string matching

There are numerous algorithms for finding matches between strings and patterns, see wikipedia for detailed explanations. In the example implementation below, I chose a simpler variation of the Boyer-Moore algorithm, just because it's fast to implement and understand, and good enough in practice. The algorithm is called Boyer–Moore–Horspool algorithm or Horspool's algorithm.

It uses only the first table from Boyer-Moore, which is why it's easy to implement.
First, here's the function which build the table:

   1:  const int SIZE = 255;

   2:   

   3:  void computeTable(int arr[], char* pattern, int len) {

   4:      for (int i = 0; i < SIZE; i++) {

   5:          arr[i] = len;

   6:      }

   7:      for (int i = 0; i < len - 1; i++) {

   8:          arr[pattern[i]] = len - i - 1;

   9:      }

  10:  }

And the actual string matching uses the table which we build above:

   1:  int findOccurences(char* pattern, int patternLen, char* str, int strLen, int* table) {

   2:      int i = 0;

   3:      int pos = 0;

   4:      int last = patternLen - 1;

   5:      while (patternLen <= strLen) {

   6:          for (i = last; str[i] == pattern[i] && i >= 0; i--);

   7:          if (i == -1)

   8:              //return pos;

   9:              cout << "found one at position: " << pos << endl;

  10:          if (strLen <= table[str[last]])

  11:              return -1;

  12:          int offset = table[str[last]];

  13:          str += offset;

  14:          strLen -= offset;

  15:          pos += offset;

  16:      }

  17:      return -1;

  18:  }

You can use it simply by typing this:

   1:  int main() {

   2:      char pattern[] = "gcagagag";

   3:      char str[] = "gcatcgcagagagtatacagtacg";

   4:      int patternSize = sizeof(pattern) - 1;

   5:      int strSize = sizeof(str) - 1;

   6:      int arr[SIZE];

   7:      computeTable(arr, pattern, patternSize);

   8:      cout << "Finding occurences... " << endl;

   9:      cout << findOccurences(pattern, patternSize, str, strSize, arr) << endl;

  10:      return 0;

  11:  }