Thread: reversing elements of array using a pointer

this is my source code why wont it reverse it??? all it does is print it out the same way as before.....help its due tommorow thanx.....

#include <stdio.h>

#define MAX 5

void exchange(int *pAry,int *first,int size);

int main (void)
{
int ary[MAX]={6,82,7,3,21};
int *pWalk;
int *pLast;

pLast = ary + MAX - 1;

printf("Your Elements:\n");
for( pWalk=ary; pWalk<=pLast; pWalk++ )
printf("%3d",*pWalk);
printf("\n\n");

exchange (ary,pWalk,MAX-1);

printf("Your Elements in Reverse:\n");
for ( pWalk=ary; pWalk<=pLast; pWalk++ )
printf("%3d",*pWalk);
printf("\n\n");

return 0;
}

void exchange (int *pAry,int *first,int size)
{
int *temp;
int *mid;
int *pLast;

mid = (pAry+3);
pLast = pAry + size - 1;

for ( first=pAry; first<mid; first++, pLast--)
{
temp=first;
first=pLast;
pLast=first;
}

return;
}

For one, change declarations like this:

pLast = ary + MAX - 1;

To

pLast = &ary[MAX - 1];

Try this for similar 'pLast' and 'pWalk' (if needed) declarations.

Why? "pLast = ary + MAX - 1; " is very clear, this really shows that you understand calculating with pointers.

Wrong is the reversing function. This one is better.

Code:

void reverse (int *array, int size)
{
    int temp;
    int index;  
   
    for (index = 0; index < (size / 2); index++)
    {
            temp = array [index];
            array [index] = array [size - index - 1];
            array [size - index - 1] = temp;
    }
}

A hint about debugging. Use printf's. Use them to display important data at certain places in the code. You can also use them to debug pointer calculations, if a pointer p is declared as int *p, then printf ("%d\n", p); prints out the address. So in that way you can check if calculations are going right.

thanx shiro i got it to finnaly work.....