#include <iostream>
using namespace std;
int main()
{
    int a,b;
    cin >>a;
    if (a>=1){
        for (int i=1;i<=a;i++){
            b=b+i;
        }
    }
    else if (a<1){
        for (int i=1;i>=a;i--){
            b=b+i;
        }
    }
    cout<<b;
}


i tested with test case #1 it work, but after submit the judge says wrong answer test 1, why?

b initial value is?

Do you use gcc? Probably "-Wuninitialized" option can help.