例2-7+例2-8

#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
",sum);

    return 0;
}

/*计算1+2+3+...+n*/
#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;
    }
    /*输出累加和*/
    printf("Sum of numbers  from 1 to %d is %d
",n,sum);

    return 0;
}