my cpp file
#include <stdio.h>

int main(){
    int num;
    int answer;
    scanf("%d",&num);
    if(num>=0){
    for(;num>=1;num--)
    answer += num;
    }
    else{
    for(;num<=-2;num++)
    answer += num;
    }
    printf("%d\n",answer);
    return 0;
    }
where is the wrong ?

1) int answer;  // wrong
int answer = 0; // right
2) for 0 answer is 1, not 0

thank you ! I have known where is wrong .thank you all the same!