2-7

/* 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",n,sum);


    return 0;
}