为啥定义在main函数外边对，里面就不对？

#include <stdio.h>

int T;
long long N, k, sum;
int main()
{
  /* int T;               */
  /* long long N, k, sum; */
  scanf("%d", &T);

  while (T--)
  {
    scanf("%d%d", &N, &k);
    sum = (1 + k) * k / 2;
    if (N >= sum)
      printf("Yes\n");
    else
      printf("No\n");
  }

  return 0;
}