I'm bad help me why doesn't this work

Code:

---

#include <iostream>
using namespace std;

int main() {
    int x;
    int a, b;

    cout << "welcome to the calculator" << endl;
    cout << "enter 1 for division, 2 for multiplication, 3 for addition and 4 for subtraction" << endl;
    cin >> x;

    int sum;

    if (x == 1) {
        sum = a / b;
    }

    if (x == 2) {
        sum = a * b;
    }

    if (x == 3) {
        sum = a + b;
    }

    if (x == 4) {
        sum = a - b;
    }

    cout << "enter a number" << endl;
    cin >> a;

    cout << "one more please" << endl;
    cin >> b;

    cout << "and your answer is!" << endl;
    cout << sum;

    return 0;
}

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It just says - 37 or 0. I want it to be able to calculate stuff

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You first define the variables a and b without specifying their values. You then use them in calculations to produce a value for sum. Then after the calculations you ask the user to input the values for a and b. However the entered values are not used as the input comes after they are used. You need to have the cout/cin statements referring to a and b before these variables are used in the calculation for sum.