Thread: ??? Any Suggestions for Speeding This Up ???

I recently made a program that looks for quadratic equations (ax²+bx+c = N) that, when incremented values of x are inputted, generate a lot of prime numbers. The problem is, when going for 10000 or 100000 different values for x, it has to check each result N for primality, which is slow. Plus, it checks for all combinations of a, b, and c, over a range, which REALLY slows it down.

Any suggestions for speeding up this program at all? Even a little bit will speed it up, because this is on the order of millions or billions of math calculations and loops.

Thanks.

Code:

#include <iostream>
#include <string>
#include <cstdlib>
#include <stdio.h>
#include <math.h>
#include <ctype.h>

using namespace std;

void main(){
	
	
	short amin;
	short amax;
	short bmin;
	short bmax;
	short cmin;
	short cmax;
	short iterations;
	float pmin;
	float pmax;


	cout << "ax^2 + bx + c" << endl;
	cout << " " << endl;

	//RANGE FOR A
	cout << "Range for a? (integers -32,768 to 32,767)" << endl;
	cout << " " << endl;
	cout << "min? ";
	cin >> amin;
	cout << " " << endl;
	cout << "max? ";
	cin >> amax;
	cout << " " << endl;
	cout << " " << endl;

	//RANGE FOR B
	cout << "Range for b? (integers -32,768 to 32,767)" << endl;
	cout << " " << endl;
	cout << "min? ";
	cin >> bmin;
	cout << " " << endl;
	cout << "max? ";
	cin >> bmax;
	cout << " " << endl;
	cout << " " << endl;
	
	//RANGE FOR C 
	cout << "Range for c? (integers -32,768 to 32,767)" << endl;
	cout << " " << endl;
	cout << "min? ";
	cin >> cmin;
	cout << " " << endl;
	cout << "max? ";
	cin >> cmax;
	cout << " " << endl;
	cout << " " << endl;


	//ITERATIONS

	cout << "How many iterations? (no more than 65,535)" << endl;
	cin >> iterations;
	cout << " " << endl;
	cout << " " << endl;

  	
	//PERCENTAGE PRIME

	cout << "What percentage should be Prime? (integer 0 to 100)" << endl;
	cout << " " << endl;
	cout << "min? ";
	cin >> pmin;
	cout << " " << endl;
	cout << "max? ";
	cin >> pmax;
	cout << " " << endl;
	cout << " " << endl;

	cout << "Wait..." << endl;
	cout << " " << endl;
	cout << " " << endl;

	float percentmin = pmin/100;
	float percentmax = pmax/100;
	

	//START

	//Values for A
	for (short a = amin; a <= amax; a++)
	{
		
		if(a==0)	//skips the linears
		{
		}
		
		
		else
		{
			//Values for B
			for (short b = bmin; b <= bmax; b++)	//CHANGE BACK TO b++
			{
			
				//Values for C
				for (short c = cmin; c <= cmax; c++)	//CHANGE BACK TO c++
				{		
				
					//keeps track of how many primes result for this quadratic
					unsigned short primes = 0;	

					//keeps track of the total iterations for this quadratic
					unsigned short total = 0;	
				
					//START of test for increasing values of i
					for(short i=0;i<iterations;i++)
					{
			

						short flag = 0;

						__int64 n = ((a*i*i) + (b*i) + c);
		
						if(n>1)
						{
							if((n%2)==0)	//checks against 2
							{		

								flag = 1;
							}
			
							else
							{

								// checks odds from 3 up to sqrt(n)
								for(long m = 3;m<=((long)(sqrt(n)));m+=2)	
								{	
				
									if((n%m)==0)
									{	 
					
										flag = 1;
										break;
			
									}

								}

							}
		
		
							if(flag==0)
							{

								primes = primes + 1;

							}

							total++;

						}

						else
						{
							/*cout << " " << endl;
							cout << "---------------------------------------" << endl;
							cout << n << " was tossed out for being <= 1..." << endl;
							cout << "---------------------------------------" << endl;
							cout << " " << endl;*/
						}

		
					}

					double primepercent =  ((double) primes) /(iterations);

					if((primepercent >= percentmin) && (primepercent <= percentmax))
					{
					

						cout << " " << endl;
						cout << a << "x^2 + " << b << "x + " << c << endl;
						cout << primes << " out of " << total << " were prime." << endl;
					
	
						//cout << primes << endl;
					
					}

				}

			}
		
		}

	}
	
}