Lucky numbers

input/code.cpp: In function 'int main()':
input/code.cpp:15:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int col =0; col < s.size(); col++) inp[col] = s[col] - '0';
                                   ^
input/code.cpp:23:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int col =1; col < s.size(); col++) {
                                   ^
input/code.cpp:35:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (col + 1 == s.size()) {
                                   ^

#include <vector>
#include <utility>
#include <algorithm>
#include <iostream>
using namespace std;

int main() {
    string s; cin >> s;
    if (s.size() == 1) {
        cout << 0; return 0;
    }
    vector<int> inp(s.size());
    for (int col =0; col < s.size(); col++) inp[col] = s[col] - '0';
    vector<vector<int>> dp(10,vector<int>(s.size(), 1e9));
    for (int row=0; row < 10; row++) {
        dp[row][0] = 1;
    }
    dp[inp[0]][0] = 0;

    int ans = 1e9;
    for (int col =1; col < s.size(); col++) {
        for (int row=0; row < 10; row++) {
            for (int prev=0; prev< 10; prev++) {
                if ((row + prev) % 7 == 0) {
                    int cand1 = dp[prev][col-1];
                    //cout << dp[col][col] << "qq" <<endl;
                    if (row != inp[col]) cand1++;
                    //cout << cand1 << " " << dp[row][col] << " qq " << row << " " << prev <<endl;
                    dp[row][col] = min(dp[row][col], cand1);
                    //cout << cand1 << " " << dp[row][col] << " qq2 " << row << " " << prev<<endl;
                }
            }
            if (col + 1 == s.size()) {
                //cout << dp[row][col] << "qwe" <<endl;
                ans = min(ans, dp[row][col]);
            }
        }
    }
    cout << ans;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED