#include<stdio.h>
int main()
{
    int n,a,b,c,s;
    while(scanf("%d",&n)!=EOF)
    {
        if(n>=3)
        {
            scanf("%d %d %d",&a,&b,&c);
            s=a+b+c;
            printf("%d\n",s);
        }
        else if(n=2)
        {
            scanf("%d %d",&a,&b);
            s=a+b+10;
            printf("%d\n",s);
        }
        else if(n=1)
        {
            scanf("%d",&a);
            s=a+20;
            printf("%d\n",s);
        }
    }
    return 0;
}
错误如题，都有循环，为什么最后一个输不出

判断变量和常量是否相等，else if这个条件一直为TRUE

else if(n==2);
else if(n==1);
程序里等是 ==
刚刚试了，可以。
#include<stdio.h>
int main()
{
    int n,a,b,c,s;
    while(scanf("%d",&n)!=EOF)
    {
        if(n>=3)
        {
            scanf("%d %d %d",&a,&b,&c);
            s=a+b+c;
            printf("%d\n",s);
        }
        else if(n==2)
        {
            scanf("%d %d",&a,&b);
            s=a+b+10;
            printf("%d\n",s);
        }
        else if(n==1)
        {
            scanf("%d",&a);
            s=a+20;
            printf("%d\n",s);
        }
    }
    return 0;
}

if(n=2)
 改成if(n==2) 两个等号

谢啦