第二章例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,sum);

 return 0;
}