Printing out variables in c changes values of variables
- by George Wilson
I have an odd problem with some c-programme here. I was getting some wrong values in a matrix I was finding the determinant of and so I started printing variables - yet found that by printing values out the actual values in the code changed.
I eventually narrowed it down to one specific printf statement - highlighted in the code below. If I comment out this line then I start getting incorrect values in my determinent calculations, yet by printing it out I get the value out I expect
Code below:
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#define NUMBER 15
double determinant_calculation(int size, double array[NUMBER][NUMBER]);
int main() {
double array[NUMBER][NUMBER], determinant_value;
int size;
array[0][0]=1;
array[0][1]=2;
array[0][2]=3;
array[1][0]=4;
array[1][1]=5;
array[1][2]=6;
array[2][0]=7;
array[2][1]=8;
array[2][2]=10;
size=3;
determinant_value=determinant_calculation(size, array);
printf("\n\n\n\n\n\nDeterminant value is %lf \n\n\n\n\n\n", determinant_value);
return 0;
}
double determinant_calculation(int size, double array[NUMBER][NUMBER])
{
double determinant_matrix[NUMBER][NUMBER], determinant_value;
int x, y, count=0, sign=1, i, j;
/*initialises the array*/
for (i=0; i<(NUMBER); i++)
{
for(j=0; j<(NUMBER); j++)
{
determinant_matrix[i][j]=0;
}
}
/*does the re-cursion method*/
for (count=0; count<size; count++)
{
x=0;
y=0;
for (i=0; i<size; i++)
{
for(j=0; j<size; j++)
{
if (i!=0&&j!=count)
{
determinant_matrix[x][y]=array[i][j];
if (y<(size-2)) {
y++;
} else {
y=0;
x++;
}
}
}
}
//commenting this for loop out changes the values of the code determinent prints -7 when commented out and -3 (expected) when included!
for (i=0; i<size; i++) {
for(j=0; j<size; j++){
printf("%lf ", determinant_matrix[i][j]);
}
printf("\n");
}
if(size>2) {
determinant_value+=sign*(array[0][count]*determinant_calculation(size-1 ,determinant_matrix));
} else {
determinant_value+=sign*(array[0][count]*determinant_matrix[0][0]);
}
sign=-1*sign;
}
return (determinant_value);
}
I know its not the prettiest (or best way) of doing what I'm doing with this code but it's what I've been given - so can't make huge changes. I don't suppose anyone could explain why printing out the variables can actually change the values? or how to fix it because ideally i don't want to!!
