A Challenging Debugging Problem

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Join Date: Oct 2006

Location: India

Posts: 514

Reputation: Jishnu will become famous soon enough

Rep Power: 5

Solved Threads: 25

Jishnu

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A Challenging Debugging Problem

Jun 4th, 2007

Hello,

The code below calculates the determinant of the matrix. I know that the method of global 2-d pointers is a poor programming practice (so u don't need to reply saying that!!!), but it is a simple method for an amateur programmer. As the code didn't work, I set two watches,
(After giving the input as a 3x3 matrix with elements numbered from 1 to 9) one on e[k][l] & another on b[k1][l1]. To my surprise, b[k1][l1] got modified on its own inspite the fact that e[k][l] at k=1 and l=1 had the value of 5.

Somebody plz help me out.

-Jishnu.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include<iostream.h>
#include<iomanip.h>
#include<conio.h>
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
void show(float **a,int n);
float det(float **b,int n);
void minor(float **a,int o,int i,int j);
void main()
{
clrscr();
int o,i,j;
float **a,ans;
cout<<"Enter The Order Of Matrix:";
cin>>o;
for(i=0;i<o;i++)
a[i]=new float[o];
for(i=0;i<o;i++)
for(j=0;j<o;j++)
cin>>a[i][j];
ans=det(a,o);
cout<<ans;
getch();
}
void show(float **a,int n)
{
cout<<"\n";
for(int i=0;i<n;i++)
{
for(int j=0;j<n;j++)
{cout<<setw(8)<<a[i][j]<<" ";}
cout<<"\n\n";
}
}
float **b;
float det(float **c,int n)
{
float ans=0;
float *d;
d=new float[n];
for(int i=0;i<n;i++)
d[i]=c[0][i];
if(n>2)
{
for(int i=0;i<n;i++)
{
minor(c,n,0,i);
if(i%2==0)
ans+=d[i]*det(b,n-1);
else
ans-=d[i]*det(b,n-1); 
}
}
if(n==2)
{
return(c[0][0]*c[1][1]-c[0][1]*c[1][0]);
}
return ans;
}
void minor(float **e,int o,int i,int j)
{
int k1=0,l1;
for(int k=0;k<o;k++)
{
l1=0;
for(int l=0;l<o;l++)
{
if(k==i)
{k1--;break;}
if(l==j)
continue;
[b][color=red]b[k1][l1]=e[k][l];:-O [/color][/b]
l1++;
}
k1++;
}
}
#include<iostream.h>
#include<iomanip.h>
#include<conio.h>
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
void show(float **a,int n);
float det(float **b,int n);
void minor(float **a,int o,int i,int j);
void main()
{
clrscr();
int o,i,j;
float **a,ans;
cout<<"Enter The Order Of Matrix:";
cin>>o;
for(i=0;i<o;i++)
a[i]=new float[o];
for(i=0;i<o;i++)
for(j=0;j<o;j++)
cin>>a[i][j];
ans=det(a,o);
cout<<ans;
getch();
}
void show(float **a,int n)
{
cout<<"\n";
for(int i=0;i<n;i++)
{
for(int j=0;j<n;j++)
{cout<<setw(8)<<a[i][j]<<" ";}
cout<<"\n\n";
}
}
float **b;
float det(float **c,int n)
{
float ans=0;
float *d;
d=new float[n];
for(int i=0;i<n;i++)
d[i]=c[0][i];
if(n>2)
{
for(int i=0;i<n;i++)
{
minor(c,n,0,i);
if(i%2==0)
ans+=d[i]*det(b,n-1);
else
ans-=d[i]*det(b,n-1); 
}
}
if(n==2)
{
return(c[0][0]*c[1][1]-c[0][1]*c[1][0]);
}
return ans;
}
void minor(float **e,int o,int i,int j)
{
int k1=0,l1;
for(int k=0;k<o;k++)
{
l1=0;
for(int l=0;l<o;l++)
{
if(k==i)
{k1--;break;}
if(l==j)
continue;
[b][color=red]b[k1][l1]=e[k][l];:-O [/color][/b]
l1++;
}
k1++;
}
}