swap columns in two dimensional array with pointers

[lio]

Hi ,trying to swap columns in two dimensional array with pointers
fswap-first column to swap
sswap-second column to swap
What am I doing wrong
Thank you

void swapColumns(double a[][6],int row,int col,int fswap,int sswap)
 {
    int i;
    double *px,temp;
    px=a;
   for (i=0;i<row ;i++) 
   {   
     temp=*(px+fswap);
     *(px row*col+fswap) = *(px row*col+sswa)p;
     *(px row*col+sswap)=temp; 
   }  
  }

[Adak]

How are you going to "walk" down the column, without your loop iterator being involved?

Every time you loop, you change i, and nothing else. But you loop logic doesn't use i at all.

[lio]

I changed it but still dont work

void swapColumns(double a[][6],int row,int col,int fswap,int sswap)
 {
    int i;
    double *px,*temp;
    px=a;
   for (i=0;i<row ;i++) 
   {   
      temp=*(px i*col+fswap);
     *(px i*col+fswap) = *(px i*col+sswap);
     *(px i*col+sswap)=temp; 
   }  
  }

[Salem]

What exactly are you trying to swap?

> px=a;
In particular, why are you using a bone-headed approach like this, when you already have the ability to index the array using [r][c] notation.
It would certainly simplify your code.

temp = a[i][from];
a[i][from] = a[i][to];
a[i][to] = temp;

[lio]

I am trying to swap two columns in two dimensional array(lets say second and forth).And I have to use pointers and pointer arithmetic

[Salem]

> temp=*(px i*col+fswap);
And C doesn't have a 'space' operator.

Maybe write it the obvious way first, just to make sure it ACTUALLY works, then try to mung it to how your "prof" would like it.

[lio]

I did write it the obvious way ,but when I go with pointers is giving mi errors

 void swapColumns(double a[][6],int row,int col,int fswap,int sswap)
 {
    int i;
    double temp;
   for (i=0;i<row ;i++) 
   {   
     temp=a[i][fswap];
     a[i][fswap]=a[i][sswap];
     a[i][sswap]=temp; 
   }  
  }

POinters -sintax error before i

void swapColumns(double a[][6],int row,int col,int fswap,int sswap)
 {
    int i;
    double *px,*temp;
    px=a;
   for (i=0;i<row ;i++) 
   {   
      temp=*(px i*col+fswap);
     *(px i*col+fswap) = *(px i*col+sswap);
     *(px i*col+sswap)=temp; 
   }  
  }

[laserlight]

As Salem noted, there is no 'space' operator, so syntax like px i is wrong (except in some special cases).

[lio]

Is there a way to fix that

[laserlight]

Just leave it in index notation.

[lio]

Thanks ,But I still don't understand
Could you give me an example

[Salem]

Perhaps you meant to add the calculated offset?