Question

I can’t get the codes right.
Can somebody help?

#include<stdio.h>
int main()
{
 int n, sum,i,j;

 printf("Please enter an integer, n = ");
 scanf("%d", &n);

 for(i=1;i<=n;i++)
     for(j=1;j<=i;j++)
         sum = sum + n;
 printf("sum = %d", sum);


 return 0;
}

Answer 1

1. You are not initialising sum. Initialise it with 0.
2. You shouldn’t be adding n at each step, but j.

Of course, this is to fix your current code. There are better approaches to solving the problem, which others have already mentioned.

Edit:

Just for fun, here’s a formula that allows you to solve the problem in O(1):

Your sum is equal to n*(n + 1)*(2*n + 1) / 12 + n*(n + 1) / 4.

This is obtained by writing it as a sum and using the fact that the sum of the first n consecutive squares is n(n + 1)(2n + 1) / 6 and the sum of the first n positive ints is n(n + 1)/2. +1 if you can find a nicer form of the formula.