1.

#include<stdio.h>
int main()
{
    int i,n,sum=0;
    printf("Enter Your Number:");
    scanf("%d",&n);
    i=1;
    while(i<=n)
    {
        if(i%2==0)
        {
            sum=sum+i;
        }
        i++;
    }
    printf("Sum Of Even Numbers = %d\n",sum);
    return 0;
}