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C Exercises: Find the largest prime factor of the number 438927456

C Programming Practice: Exercise-19 with Solution

The prime factors of 13195 are 5, 7, 13, 29.
Write a C programming to find the largest prime factor of the number 438927456?.

C Code:

#include <stdio.h>
int main(void)
{
  unsigned long long n = 438927456L;
  unsigned long long i;
  for (i = 2ULL; i < n; i++) {
  	//1ULL is 'unsigned long long
    while (n % i == 0) {
      n /= i;
    }
  }
  printf("%llu\n", n);
  return 0;
}

Sample Output:

415651

Flowchart:

C Programming Flowchart: Find the largest prime factor of the number 438927456.

C Programming Code Editor:

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Previous: Write a C programming to find the sum of the even-valued terms from the terms in the Fibonacci sequence whose values do not exceed one million.
Next: Write a C programming to find the largest palindrome made from the product of two 3-digit numbers.

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