TheAlgorithms-C/project_euler/problem_1/sol1.c

/*An Efficient code to print all the sum of all numbers that are multiples of 3 & 5 below N.*/

#include <stdio.h>

int main(){
    int t; 
    printf("Enter number of times you want to try");
    scanf("%d",&t);
    while(t--)
    {
        unsigned long long N,p=0,sum=0;	
        printf("Enter the value of N ");
         
        scanf("%lld",&N);	//Take input of N from user
        p = (N-1)/3;
        sum = ((3*p*(p+1))/2);

        p = (N-1)/5;
        sum = sum + ((5*p*(p+1))/2);

        p = (N-1)/15;
        sum = sum - ((15*p*(p+1))/2);
        printf("%lld\n", sum);		//print the sum of all numbers that are multiples of 3 & 5 below N
    }
    return 0;
}