20131001国庆作业例2-7,2-8,2-9

2-7

#include<stdio.h>
int main(void)
{
    int i,n,sum;

    printf("Enter n:");
    scanf("%d",&n);
    sum=0;
    for(i=1;i<=n;i++){
        sum=sum+i;
    }
    printf("Sum of numbers from 1 to %d is %d\n",n,sum);


    return 0;
}

 

2-8

执行结果1

执行结果2

#include<stdio.h>
int main(void)
{
    int denominator,flag,i,n;
    double item,sum;

    printf("Enter n:");
    scanf("%d",&n);
    flag=1;
    denominator=1;
    sum=0;
    for(i=1;i<=n;i++){
        item=flag*1.0/denominator;
        sum=sum+item;
        flag=-flag;
        denominator=denominator+2;
    }
    printf("sum=%f\n",sum);


    return 0;
}

 

 

2-9

#include<stdio.h>
int main(void)
{
    int i,n;
    double product;


    printf("Enter n:");
    scanf("%d",&n);
    product=1;
    for(i=1;i<=n;i++){
        product=product*i;
    }
    printf("product=%.0f\n",product);


    return 0;
}