Thread: math.h question

Post a more complete example of what you're trying to do.

Well, the program is not very long, so I suppose I can simply post it in its entirety. Please bear with me; this is my first time using code tags, and I am not entirely sure that I am posting correctly.

The intent of the program is to take the scanned number, q, and print its prime factors. The problem is apparently occurring in the while loop, which is intended to remove and print each factor.

Code:

#include <stdio.h>
#include <math.h>

main()
{
	int d = 1, q, p, e = 0;
	float k;

	scanf( "%d", &q);
	for( d <= (sqrt(p)); ++d;) {
		p = q;
		k = p / d;
		while( round(k) == k) {
			e = d;
			printf("%d ", e);
			p = k;
			k = p / d;
		}
	}
	if( p == q )
		printf( "%d ", q);
	if( p != q && p != 1 )
		printf( "%d ", p);
}

1) main returns an int.
2) 'p' is uninitialized
3) Your for-loop is set up incorrectly. It should be: for( /*initialization*/; /*comparison*/; /*increment*/ )
4) The sense of the for-loop comparison should be reversed, eg: loop until 'd' reaches sqrt(q) (note: not 'p'!)
5) Fix those problems, and then print the value of each variable each iteration of the loop so that you can spot the many logic errors in the program.

>> To what does that refer?

The C standard mandates that 'main' return an int. Some compilers allow you to omit it, either by extension or simply because they're broken.

You got it.

Well, I got tired of my ineffectual attempts to fix the problem, so i rewrote it, making the variables' names a bit easier to remember, and thereby work with. However, my infinite loop problem continues. Any number that I input that bypasses the while loop returns the "prime" result, and anything else prints a continual sequence of twos.

I believe the problem may lie in the highlighted line, but I am not sure.

Code:

#include <stdio.h>
#include <math.h>

int main()
{
	int number, factor = 2;
	float remain, valid = 1, test;

	printf("Enter number\n");
	scanf("%d", &number);
	remain = number;

	while(factor <= sqrt(number)) {
		test = number / factor;
		valid = round(test) - test;
		if(valid == 0) {
			remain = test;
			printf("%d", factor);
			remain = remain / factor;
		}
		else factor = factor + 1;
	}

	if(remain == number)
		printf("prime\n");
	if(remain != number && remain != 1)
		printf("%.0f", remain);
}

Just a side note: the reason I used only letters in the first draft was that I was transposing this program from another programming language, which only allows them.