请问这还用解释吗？

#include <bits/stdc++.h>
using namespace std;
int n, h[4][13], ans;
string s;
int main()
{
    scanf("%d", &n);
    while (n--)
    {
        cin >> s;
        char a = s[0], b = s[1];
        int c;
        if (b == 'T') c = 9;
        else if (b == 'J') c = 10;
        else if (b == 'Q') c = 11;
        else if (b == 'K') c = 12;
        else if (b == 'A') c = 0;
        else c = b - 49;
        if (a == 'C') h[0][c]++;
        else if (a == 'D') h[1][c]++;
        else if (a == 'S') h[2][c]++;
        else h[3][c]++;
    }
    for (int i = 0; i < 4; i++)
        for (int j = 0; j < 13; j++) ans += !h[i][j];
    printf("%d", ans);
    return 0;
}