What makes the difference between declaring variable = 0 and leaving variable by itself?

Question

I was looking through 'while loop' and figured that the result was different when I declared variables = 0 and when I did not in the loop.

I am not sure why it makes different result...

Here`s example!

#include<stdio.h>
int main(){

    int even=0;
    int total=0;

    do{
        total+=even;
        even+=2;
    }while(even<=100);

    printf("total : %d", total);

    return 0;

}

result total : 2550

#include<stdio.h>    
int main(){

    int even;
    int total;

    do{
        total+=even;
        even+=2;
    }while(even<=100);

    printf("total : %d", total);

    return 0;

}

result total:2551

Because... you did not assign a value. In the second case, what do you think the value of `even` and `total` are before you sum them? — Weather Vane, Feb 18 '21 at 15:23

score 0 · Answer 1 · answered Feb 18 '21 at 15:24

0

The following is undefined behaviour:

int even;
int total;
total += even;

Before reading from a variable with automatic storage duration, you must initialize it or assign to it.

answered Feb 18 '21 at 15:24

ikegami

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What makes the difference between declaring variable = 0 and leaving variable by itself?

1 Answers1