#include<stdio.h>
int main()
{
    int a,b,c,d;
    double ave,sum;
    printf("请输入4个整数:\n");
    scanf("%d%d%d%d",&a,&b,&c,&d);
    sum=a+b+c+d;
    ave=sum/4;
    printf("ave=%.1f\n",ave);
    printf("sum=%.0f\n",sum);
    return 0;
}

#include<stdio.h>
#include<math.h>
int main()
{
    double x,sum;
    printf("Enter x:");
    scanf("%lf",&x);
    if(x>0&&x<=50)
    {
        printf("sum=%.2f\n",sum=0.53*x);
    }       
    else if(x>50)
    {
        
        printf("sum=%.2f\n",sum=50*0.53+(x-50)*0.58);
    }
    else
    {
        printf("无效!");
    }
        return 0;
} 

#include<stdio.h>
int main()
{
    int i,a,b,sum1,sum2,denominator;
    double item,sum;
    printf("Enter b:");
    scanf("%d",&b);
    printf("Enter a:");
    scanf("%d",&a);
    sum=sum1=sum2=0;
    for(i=b;i<=a;i++)
    {
        sum1=sum1+b*b;    
    }
    for(i=b;i<=a;i++)
    {
        item=1.0/denominator;
        sum2=sum2+item;
        denominator=denominator+1;
    }
    sum=sum1+sum2;
    printf("Sum of number from %d to %d is %.6lf\n",b,a,sum);
    return 0;
}

#include<stdio.h>
int main()
{
    int denominator=1,flag=1,i,n;
    double item,sum=0;
    printf("Enter n:");
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        item=flag*i*1.0/denominator;
        sum=sum+item;
        flag=-flag;
        denominator=denominator+2;
    }
    printf("sum=%f\n",sum);
    return 0;
}

#include<stdio.h>
#include<math.h> 
int main ()
{
    int i,n;
    double y,sum=0;
    printf ("Enter n:");
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        y=sqrt(i);
        sum=sum+y;    
    }
    printf("sum=%.2lf\n",sum);
    return 0;
}

#include<stdio.h>
double fact(int n);
int main()
{
    int i,n;
    double sum=0;
    printf("Enter n:");
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        sum=sum+fact(i);
    }
    printf("sum=%.0lf\n",sum);
    return 0;
}
double fact(int n)
{
    int i;
    double product=1;
    for(i=1;i<=n;i++)
    {
        product=product*i;
    }
    return product;
}