Problem with running c /cpp code in vscode-CodePudding

This two code I wrote should output the same thing, but I don't know why, when I use Function to write it, I have to put a totalDays[0] -= 1; in the line 13, and when I use Class to write it, it just works as I intended. (This problem only occurs with vscode, when I use Dev c , it just works fine without line 13)

Sample input:
20101010
20101015
First code output: 4 (without line 13)
Second code output: 5 (correct output)

First code :

#include <iostream>
using namespace std;

const int monthDays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

int countDays(int d[], int m[], int y[]) {
    int totalDays[2];
    for (int i = 0; i < 2; i  ) {
        totalDays[i]  = d[i]   365 * y[i];
        for (int j = 0; j < m[i] - 1; j  )
            totalDays[i]  = monthDays[j];
    }
    totalDays[0] -= 1;
    if (totalDays[0] > totalDays[1]) {
        return totalDays[0] - totalDays[1];
    } else {
        return totalDays[1] - totalDays[0];
    }
}

int main() {
    int d[2], m[2], y[2], yyyymmdd;
    for(int i = 0; i < 2; i  ){
        cin >> yyyymmdd;
        d[i] = yyyymmdd % 100;
        m[i] = (yyyymmdd / 100) % 100;
        y[i] = yyyymmdd / 10000;
    }

    cout << countDays(d, m, y);

    return 0;
}

Second code :

#include <iostream>
using namespace std;

class Solution {
   public:
    const int monthDays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

    int countDays(int d[], int m[], int y[], int totalDays[]) {
        for (int i = 0; i < 2; i  ) {
            totalDays[i]  = d[i]   365 * y[i];
            for (int j = 0; j < m[i] - 1; j  )
                totalDays[i]  = monthDays[j];
        }

        if (totalDays[0] > totalDays[1]) {
            return totalDays[0] - totalDays[1];
        } else {
            return totalDays[1] - totalDays[0];
        }
    }
};

int main() {
    int d[2], m[2], y[2], yyyymmdd, totalDays[2];
    for(int i = 0; i < 2; i  ){
        cin >> yyyymmdd;
        d[i] = yyyymmdd % 100;
        m[i] = (yyyymmdd / 100) % 100;
        y[i] = yyyymmdd / 10000;
        totalDays[i] = 0;
    }

    Solution ob;
    cout << ob.countDays(d, m, y, totalDays);

    return 0;
}

CodePudding user response：

Answer from David C. Rankin 4 hours ago

Your code exhibits Undefined Behavior. int totalDays[2]; is an Uninitialized array when totalDays[i] = d[i] 365 * y[i]; is called. At least do int totalDays[2] = {0}; Also compile with -Wshadow enabled, you shadow the array totalDays between main() and your function in the second example. Choose a new name for the parameter totalDays in the second case.