longest common str

#include <vector>
#include <iostream>
#include <string>
using namespace std;

int longest_common_string(string& str_a, string& str_b) {
    int len_a = str_a.length();
    int len_b = str_b.length();
    if ( == len_a ||  == len_b) {
        return ;
    }
    int rows = len_a + ;
    int cols = len_b + ;
    int ** comm_len_array = new int * [rows];
    int i = ;
    for (i=; i < rows; i++) {
        comm_len_array[i] = new int[cols];
    }

    int j = ;
    for (i = ; i < rows; i++) {
        for (j = ; j < cols; j++) {
            comm_len_array[i][j] = ;
        }
    }

    int max = INT_MIN;
    int end_sub_str_a = -;
    int end_sub_str_b = -;
    for (i = ; i < rows; i++) {
        for (j = ; j < cols; j++) {
            if (str_a[i - ] == str_b[j - ]) {
                comm_len_array[i][j] = comm_len_array[i - ][j - ] + ;
            } else {
                comm_len_array[i][j] = ;
            }

            if (comm_len_array[i][j] > max) {
                max = comm_len_array[i][j];
                end_sub_str_a = i;
                end_sub_str_b = j;
            }
        }
    }

    for (i=; i < rows; i++) {
        delete[] comm_len_array[i];
    }
    delete[] comm_len_array;

    return max;
}

int main() {
    string stra = "abcedefg";
    string strb = "abcf";
    cout << longest_common_string(stra, strb) << endl;
}