为什么我这程序运行后输出是负数

Question

Answer 1

计算结果超出long long的数值范围了
long long sum=1改成 unsigned long long sum=1;
printf("%lld",sum)改成printf("%llu",sum);

#include <stdio.h>
int main()
{
    unsigned long long sum=1;
    long long i=1;
    int n;
    printf("请输入n的值：");
    scanf("%d",&n);
    while(i<=n)
    {
        sum *=i;
        i++;
    }
    printf("%llu",sum);
    return 0;
}