求指导，为啥全是WA

#include <stdio.h>
int main()
{
    int num,result;
    int sign = 1;
    scanf("%d",&num);
    if(num == 0){
        printf("%d",num);
        return 0;
    }
    if(num<0){
        sign = -1;
        num *= sign;
    }
    while(num>0){
        int unit = num%10;
        result = result*10+unit;
        num /= 10;
    }
    result *= sign;
    printf("%d",result);
    return 0;
    
}