Baffled /w C++ code: - Overclock.net

MangledWookie · 07-07-06

Im still trying to get used to C++ code and stuff. I can read it and usually understand it, but apprently i cant write it for crap

I thought that making a program that calculates primes wouuld be a decent 'getting used to it again' excercise but ive been left baffled.

Heres what i have right now:

Code:

#include <iostream.h>
#include <math.h>

int main(){
	int n;
	int i;
	int is_prime;

	is_prime = true;

	cout << "In ascending order, the prime numbers are: \n\n\n";

	for (n=3; n>0; n++)
	{
		for (i=2; i <= sqrt(double(n); i++) 
		{
			if (n%i == 0) 
				is_prime = false;
		}

		if (is_prime == true)
			cout << n << "\n";
	}
	return (0);
}

It compiles fine, but it just sits there, not giving any output.

If it something big, or you have a big suggestion for it, then post here - but if it just a small mistake, just PM me and spare me some humiliation : lachen :

Peace ppl

*Xaimus* · 07-07-06

The innermost "if statement" that determines if a number is prime or not never halts its parent "for" loop. Also, is_prime is never reset.

Code:

#include <iostream>
#include <math.h>

using namespace std;

int main() {
	int n;
	int i;
	bool is_prime = true;

	cout << "In ascending order, the prime numbers are: \n\n\n";

	for (n=3; n>0; n++)
	{
		for (i=2; i <= sqrt(double(n); i++) 
		{
			if (n%i == 0) {
				is_prime = false;
				break;
			}
		}

		if (is_prime == true)
			cout << n << "\n";

		is_prime = true;
	}
	return (0);
}

Changes in bold are corrections to logic errors. Italic changes are minor stylistic revisions.

MangledWookie · 07-08-06

Quote:

Originally Posted by Xaimus

The innermost "if statement" that determines if a number is prime or not never halts its parent "for" loop. Also, is_prime is never reset.

Code:

#include <iostream>
#include <math.h>

using namespace std;

int main() {
	int n;
	int i;
	bool is_prime = true;

	cout << "In ascending order, the prime numbers are: \n\n\n";

	for (n=3; n>0; n++)
	{
		for (i=2; i <= sqrt(double(n); i++) 
		{
			if (n%i == 0) {
				is_prime = false;
				break;
			}
		}

		if (is_prime == true)
			cout << n << "\n";

		is_prime = true;
	}
	return (0);
}

Changes in bold are corrections to logic errors. Italic changes are minor stylistic revisions.

Ah beautiful. Makes sense!. And thanks for noting the 'is_true' reset. I would have had a stroke figuring that out

Thanks alot - peace

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