What is wrong with this c code?

qanopus · 06-02-2005, 09:31 AM

Hi,

can anyone tell me what goes wrong in this code?;

Code:

void rowReduce(float points[3][2], float params[2])
{
	float mat[3][2];
	int r,c,i;

	for(r=0;r<=2;r++)
	{
		for(c=0;c<=3;c++)
		{
			if(c != 3)
			{
				mat[c][r] = pow(points[r][0],2-c);
			}
			else
			{
				mat[c][r] = points[r][1];
			}
			printf("%f ",mat[c][r]);
		}
		printf("\n");
	}
	printf("\n");

	for(r=0;r<=2;r++)
	{
		for(c=0;c<=3;c++)
		{
			printf("%f ",mat[c][r]);
		}
		printf("\n");	
	}

	free(mat);
}	

int main(int argv, char **argc)
{
	float points[3][2]= {{-10.0,1.0},{0.0,0.0},{2.0,1.0}};
	float params[2];
	int i;

	rowReduce(points,params);

	return 0;
}

When you run this code, you will see two times a set of 4 by 3 floating point numbers. These two sets should be identical, by they ar not! What's going on?

Thanks in advance....

jim mcnamara · 06-02-2005, 09:46 AM

You're lucky it doesn't segfault.

Code:

float mat[3][2];

This has three elements

You reference four elements here - you are probably overwriting the r & c variables.

Code:

for(c=0;c<=3;c++)

qanopus · 06-02-2005, 09:51 AM

Oh... oh well i'm still learing. I changed it to

Code:

mat[4][3]

. That works much better. Thanks dude

jim mcnamara · 06-02-2005, 10:04 AM

Also consider not using float - there is no extra overhead on most boxes for using double.