1+2+3+..............+n

//1+2+3+..............+n
Program:

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

Output: