Why it is assigning a garbage value to variable 'calc'?

Question

This program gives a garbage value to the variable calc .

Can anyone help me? What is the problem here?

Code:

#include <iostream>
using namespace std;

class trial {
public:
    int m1;
    int m2;
    int calc = m1 + m2;
    void setdata(int a1, int a2) {
        m1 = a1;
        m2 = a2;
    }
    void getcalc(){
        cout << "Sum of m1 & m2 is " << calc << endl;
    }
};

int main() {
    trial t1;
    t1.setdata(3, 8);
    t1.getcalc();
    system("pause>0");
    return 0;
}

Output:

Sum of m1 & m2 is -1717986920

Answer 1

The problem is how you defined calc .

When a object trial is initialized, m1+m2 is assigned to calc , but m1 and m2 are not initialized themselves (they contain 'garbage').

When setdata() is called, two user-provided integers are assigned to m1 and m2 , but calc is unchanged, thus the 'garbage' in the output.

You need to update calc by adding calc = m1 + m2; in setdata() .

Answer 2

You are never calculating the sum at first place...

void setdata(int a1, int a2) {
        m1 = a1;
        m2 = a2;
        calc = m1 + m2;
    }

but always initialize the member variables, you are not initializing the m1 and m2, hence garbage values which is assigned by the compiler.