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C Exercises: Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum

C Programming Practice: Exercise-22 with Solution

The sum of the squares of the first ten natural numbers is,
12 + 22 + ... + 102 = 385
The square of the sum of the first ten natural numbers is,
(1 + 2 + ... + 10)2 = 552 = 3025
Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 − 385 = 2640.
Write a C programming to find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

C Code:

#include <stdio.h>
int main(void)
{
  unsigned sum1 = 0, sum2 = 0, i;
  for (i = 1; i <= 100; i++) {
    sum1 += i*i;
    sum2 += i;
  }
  printf("%u\n", sum2*sum2 - sum1);
  return 0;
}

Sample Output:

25164150

Flowchart:

C Programming Flowchart: Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

C Programming Code Editor:

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What is the difficulty level of this exercise?

C Programming: Tips of the Day

C Programming - Why do all the C files written by my lecturer start with a single # on the first line?

In the very early days of pre-standardised C, if you wanted to invoke the preprocessor, then you had to write a # as the first thing in the first line of a source file. Writing only a # at the top of the file affords flexibility in the placement of the other preprocessor directives.

From an original C draft by the great Dennis Ritchie himself:

12. Compiler control lines

[...] In order to cause [the] preprocessor to be invoked, it is necessary that the very first line of the program begin with #. Since null lines are ignored by the preprocessor, this line need contain no other information.

That document makes for great reading (and allowed me to jump on this question like a mad cat).

I suspect it's the lecturer simply being sentimental - it hasn't been required certainly since ANSI C.

Ref : https://bit.ly/2Mb8OVZ