random 2-d array problem

[NSH]

I've been working on writing a program that randomly fills sites in a 2-D array (10x10) with 1's and 0's that meet a user input for the fraction of 1's sites compared to total sites. The code I wrote works in principle I think but when I compiled and ran it I had an unexpectedly long run time (i never got it to finish). Is there any errors in my coding or is it just inefficient?

the code:

#include <iostream>
#include <cmath>
#include <ctime>
#include <new>

using namespace std;

int main()
{
	//declare parameters
	
	float p; //percentage of sites filled in array
	long int i, j, n, m; // i=rows j=columns; loop indexes-n,l
	long int pmass;  //mass of percolating chain
	long int filled, unfilled; // filled=number of 1s, unfilled=number of 0s
	int perc_array[10][10]; //declare 2-d 10x10 array
	
	//set i, j to both be 10
	i=10;
	j=10;
	

	
	// user inputs
	
	cout<<"What percentage (decimal) of sites do you want filled? (no more than 3 decimal places) \n";
	cin>>p;
	
	//zero filled and unfilled variables
	filled=0;
	unfilled=0;
	
	//zero the array elements before seeding the sites. does this by going down each column and zeroing all the rows
	//after it zeroes all the rows in the first column it does it for the second..to the jth column
	for(n=0; n<j; n++)
	{
		for(m=0;m<i;m++)
			perc_array[m][n]=0;
	}
	
	//seeding random number generator
	srand(time(NULL));
	
	// fill array with 0's or 1's (1's will indicate filled sites) and have the ratio of 1's to total array size
	// be the same as the user defined p
	do
	{
		//randomly fill array with 0s and 1s
		for(n=0; n<j; n++)
		{
			for(m=0; m<i; m++)
				perc_array[m][n]=rand() % 2; //generates random 0 or 1 to fill array spot
		}
		
		//count the number of filled and unfilled sites	
		for(n=0; n<j; n++)
		{
			for(m=0; m<i; m++)
			{
				if(perc_array[m][n]==0)
					unfilled++;
				else
					filled++;
			}
		}
	} while((filled/(filled+unfilled))!=p); // recalculates the array until the (filled/total) ratio is p
	
	//output array to check by hand (for debugging purposes)
	for(n=0;n<i;n++) //does output for each row n
	{
		for(m=0;m<j;m++) //outputs all columns in each row n
		{
			cout<<perc_array[n][m];
			if(m==100)
				cout<<"/n"; //new row
		}
	}
}

[ericeps]

Probably an infinite loop. To see where it is, you could add:
cout<<"Loop ID =1"<<endl;
inside every loop (obviously change the 1 to a unique number), to see which one is repeating.

[NSH]

I did what you suggested and I found out that the do-while loop is repeating ad infinitum. I made some modifications to try and make it check the while condition clearer. So the new do while loop is:

	do
	{
		//randomly fill array with 0s and 1s
		for(m=0; m<j; m++)
		{
			for(n=0; n<i; n++)
				perc_array[m][n]=rand() % 2; //generates random 0 or 1 to fill array spot
		}
		//count the number of filled and unfilled sites	
		
		for(n=0; n<j; n++)
		{
			for(m=0; m<i; m++)
			{
				if(perc_array[m][n]==0)
				{
					unfilled++;
				}
				else if(perc_array[m][n]==1)
				{
					filled++;
				}
			}
		}

		//simplification variables
		total=100;
                randp=(filled/total);

		//reset filled and unfilled when random array isn't percentage filled user specified
		if(randp!=p)
		{
			filled=0;
			unfilled=0;
		}
		//otherwise tell user of values (randp should be same as user input)
		else if(randp==p)
			cout<<filled<<","<< unfilled<<","<<total<<","<<randp;

	} while(randp!=p); // recalculates the array until the (filled/total) ratio is p  

So, to my understanding the loop should terminate when it builds the array with the same percentage of 1's the user specified. since the condition is true when randp is not p the do-while loop will run again. However this still runs to infinity. I tried some couts and found that it is not correctly computing randp. Inside the do-while loop it says randp is 0. Even though when I have it tell me the number for filled states it returns a non-zero number. What am I doing wrong here??

[rojSarton]

When I ran your code (same as first post with only the do-while loop replaced be the second post), it seems to work fine for me. However, the variables "total" and "randp" were not declared in your first post, and so I declared them in the same line as p (ie as other floats) because I didn't know any better. My best guess would be that you have total declared as an int or long int. In C and C++, when you divide an int by an int, you get an int, even though you're trying to store it into a float or double. This is my speculation as to why you see randp as always zero due to your division statement at line 28. My method of decalring total as a float fixed the problem because if a float is part of the division, you can get a float back, but the other way is to cast one of the int's. In other words:

float d;
int b, c;

d = b/c;  //returns an int into d

d = (float) b/c; // returns a float into d 

Hope that helps.

EDIT: I meant to add that you should include <cstdlib> in addition to the other headers you have. Your compiler may not require it because it adds it automatically, but you have some function calls that need it (ie rand()).