What I want to do is:
change the array a[] = {1,2,3,4,5}
to a[] = {5,4,3,2,1}
by recursion

void reverse(int *a, int size){
if ( size == 0)
   return;
int t = a[size-1];
a[size - 1] = *a;
*a = t;
reverse(a, size/2);
}

However, the above coding did not work
it only gave the result {5,3,2,4,1}
It seems that the pointer did not progress forward after I plus 1.
i.e. it can't move from a[0] to a[1] and so on...

Thanks for your help!

Probably some thing of this sort

void rev(int* arr, int lower, int upper)
{
     if ( lower >= upper)
        return;

     // Swap the 2 values
     rev(arr, lower+1, upper-1);
}

Where lower and upper are the smallest and the largest indexes of the array

Probably some thing of this sort

void rev(int* arr, int lower, int upper)
{
     if ( lower >= upper)
        return;

     // Swap the 2 values
     rev(arr, lower+1, upper-1);
}

Where lower and upper are the smallest and the largest indexes of the array

Where are you changing the array?

void reverse(int *a, int size){
      if (size == 0)
      return;
      cout << *a;
      reverse(a+1, size-1);
}

It can successfully print out the array.
However, I found some weird thing in the DDD debugger.
After the first run
i.e.
reverse(a,5)
when it comes to the recursive call:
reverse(a+1,4), the value of *a is still fine, which is 2.
However, for the value int t, it becomes 1! which is not the value of a[4-1], I'm still searching the problem of the coding.

Edited 6 Years Ago by am5a03: n/a

@firstPerson

Where I have written swap the 2 variables that's where code has to be written to swap the 2 variables....I guess to remove ambiguity I should have written
write code to swap the 2 variables here

@am5a03

You dont want to break when the size=0, you want to break much before that ... Check out the code segment that I have posted.

:) thanks for you guys' help.
Finally I did it!

void reverse(int *a, int size){
     if ( size <= 0)
      return;
      int t = a[size-1];
     a[size - 1] = *a;
      *a = t;
      reverse(a+1, size-2);
      }

Edited 6 Years Ago by am5a03: n/a

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