Thread: Can't figure out what keeps hanging up my program

I have a simple program that is setup to create a path labled A-Z. Sometimes it works fine, however the default statement on the switch keeps getting accessed and I don't know why. Also sometimes the program just hangs like its in an endless loop. Any help would be great.

Code:

#include <cstdlib>
#include <ctime>
#include <iostream>

#define N 20
#define ALPHA 26
using namespace std;

int main(void)
{
	srand((unsigned) time(NULL));
	int step, row, col;
	char path [N][N];

	for (;;)
	{
/**** Section 1: Initializes the array to have character '.' ****/
	for (row = 0; row < N; row++)
	{
		for (col = 0; col < N; col++)
			path [row][col]='.';
	}
/**** End Section 1 ****/

/**** Section 2: Selects the path using character Capital Letters ****/
	path [row = rand() % N] [col = rand() % N]= 'A';
	for (step = 1; step < ALPHA;)
	{
		if (path [row +1][col] != '.' && path [row -1][col] != '.' 
			&& path [row][col +1] != '.' && path [row][col -1] != '.')
			break;
		switch (rand() % 4)
		{
			case 0: 
				if (path [row + 1][col] =='.' && (row + 1) >= 0 && (row + 1) < N)
				{
					row++;
					path [row] [col] = 'A' + step;
					step++;
				}
				else
				{
					break;
				}
			case 1: 
				if (path [row - 1][col] =='.' && (row - 1) >= 0 && (row - 1) < N)
				{
					row--;
					path [row] [col] = 'A' + step;
					step++;
				}
				else
				{
					break;
				}
			case 2: 
				if (path [row][col + 1] =='.' && (col + 1) >= 0 && (col +1) < N)
				{
					col++;
					path [row] [col] = 'A' + step;
					step++;						
				}
				else
				{
					break;					
				}
			case 3:
				if (path [row][col - 1] =='.' && (col - 1) >= 0 && (col -1) < N)
				{
					col--;
					path [row] [col] = 'A' + step;
					step++;
				}
				else
				{
					break;
				}
			default: printf("something is wrong here %d\n", step);
		}
	}

/**** End Section 2 ****/

/**** Section 3: Prints the path using character '.' ****/
	for (row = 0; row < N; row++)
	{
		for (col = 0; col < N; col++)
			printf("%c ",path [row][col]);
		printf("\n");
	}
/**** End Section 3 ****/

	system("pause");
	}
	return(0);
}

switch cases have fallthrough behavior. If you do not explicitly break form the switch, then code will continue running until the end of the switch statement. try this to demonstrate the problem:

Code:

        switch (rand() % 4)
        {
            case 0: 
                if (path [row + 1][col] =='.' && (row + 1) >= 0 && (row + 1) < N)
                {
                    row++;
                    path [row] [col] = 'A' + step;
                    step++;
                }
                else
                {
                    break;
                }
                puts("case 0");
            case 1: 
                if (path [row - 1][col] =='.' && (row - 1) >= 0 && (row - 1) < N)
                {
                    row--;
                    path [row] [col] = 'A' + step;
                    step++;
                }
                else
                {
                    break;
                }
                puts("case 1");
            case 2: 
                if (path [row][col + 1] =='.' && (col + 1) >= 0 && (col +1) < N)
                {
                    col++;
                    path [row] [col] = 'A' + step;
                    step++;                        
                }
                else
                {
                    break;                    
                }
                puts("case 2");
            case 3:
                if (path [row][col - 1] =='.' && (col - 1) >= 0 && (col -1) < N)
                {
                    col--;
                    path [row] [col] = 'A' + step;
                    step++;
                }
                else
                {
                    break;
                }
                puts("case 3");
            default: printf("something is wrong here %d\n", step);
                puts("default");
        }

Thanks,

I added breaks into each case statement and that seemed to solve that problem. Seems to work like a charm, however everyonce in a while it still hangs up. Here is the slightly modified code.

Code:

#include <cstdlib>
#include <ctime>
#include <iostream>

#define N 20
#define ALPHA 26
using namespace std;

int main(void)
{
	srand((unsigned) time(NULL));
	int step, row, col;
	char path [N][N];

	for (;;)
	{
/**** Section 1: Initializes the array to have character '.' ****/
	for (row = 0; row < N; row++)
	{
		for (col = 0; col < N; col++)
			path [row][col]='.';
	}
/**** End Section 1 ****/

/**** Section 2: Selects the path using character Capital Letters ****/
	path [row = rand() % N] [col = rand() % N]= 'A';
	for (step = 1; step < ALPHA;)
	{
		if (path [row +1][col] != '.' && path [row -1][col] != '.' 
			&& path [row][col +1] != '.' && path [row][col -1] != '.')
			break;
		switch (rand() % 4)
		{
			case 0: 
				if (path [row + 1][col] =='.' && (row + 1) >= 0 && (row + 1) < N)
				{
					row++;
					path [row] [col] = 'A' + step;
					step++;
				}
				else
				{
					break;
				}
				break;
			case 1: 
				if (path [row - 1][col] =='.' && (row - 1) >= 0 && (row - 1) < N)
				{
					row--;
					path [row] [col] = 'A' + step;
					step++;
				}
				else
				{
					break;
				}
				break;
			case 2: 
				if (path [row][col + 1] =='.' && (col + 1) >= 0 && (col +1) < N)
				{
					col++;
					path [row] [col] = 'A' + step;
					step++;						
				}
				else
				{
					break;					
				}
				break;
			case 3:
				if (path [row][col - 1] =='.' && (col - 1) >= 0 && (col -1) < N)
				{
					col--;
					path [row] [col] = 'A' + step;
					step++;
				}
				else
				{
					break;
				}
				break;
			default: 
				printf("something is wrong here %d\n", step);
				break;
		}
	}

/**** End Section 2 ****/

/**** Section 3: Prints the path using character '.' ****/
	for (row = 0; row < N; row++)
	{
		for (col = 0; col < N; col++)
			printf("%c ",path [row][col]);
		printf("\n");
	}
/**** End Section 3 ****/

	system("pause");
	}
	return(0);
}

oh I also got rid of the else statements since they were redundant. Thanks for that heads up as well.

what do you want it to do and what does it do?

All I am looking for is to print out a random path from A to Z one step at a time across a two dimensional array, which it does now. It seems to do exactly what I want most of the time. However sometimes it does not display the data, instead all i get is an unresponsive blinking cursor. I am trying to figure out what causes that.

Code:

if (path [row + 1][col] =='.' && (row + 1) >= 0 && (row + 1) < N)

the range check should be first, before the access.

Code:

if ((row + 1) >= 0 && (row + 1) < N && path [row + 1][col] =='.')

also, why not put the step increment outside the switch case?