Remove duplicate numbers from C array

Question

I have this void function that I call at a certain point on my main()

void calc(int dim){

 int a[dim],i,j,temp;

 for(int i=0;i<dim;i++)
  {
   printf("\n\n Type a number - [%d/%d]: \t",i+1,dim);
   scanf("%d", &a[i]);       
  }

 for(i=0;i<dim;i++)
  {

   for(j=i+1;j<dim;j++) {

    if(a[i]==a[j])
    {
     continue;    
    }

    else
      {
       temp=a[i];
       a[i]=a[j];
       a[j]=temp;
       printf("%d", a[j]);
      }
    }
  }

  for(i=0;i<dim;i++)
   printf("%d", a[i]);
}

The input paramenter dim is the dimension of the array. The code you see works perfectly because it sorts the numbers inside my array.

If the user types 4 5 8 7 5 as input numbers, I want to have an output like this: 8 7 5 4. I must remove the repeated number, so I worte:

if(a[i]==a[j])
    {
     continue;    
    }

By the way the output is still 8 7 5 5 4. How could I fix this?

possible duplicate of Algorithm: efficient way to remove duplicate integers from an array — Mgetz
– Mgetz, Commented Jul 25, 2013 at 16:36
By the way, you could look at std::vector in the C++ stl - this may help you in future if you didn't already know about it — user2138149
– user2138149, Commented Jul 25, 2013 at 16:41
Its question is tagged with C language even if it looks like c++ because of it i declaration in a loop — epsilon
– epsilon, Commented Jul 25, 2013 at 16:43
The declaration of i in a loop looks like C supported by the old standard (C99), let alone the current standard (C2011, C11). Only certain widely used C compilers are still stuck in the C89 time-warp (yes, that's MSVC). — Jonathan Leffler
– Jonathan Leffler, Commented Jul 25, 2013 at 16:56

Jonathan Leffler · Accepted Answer · 2013-07-25 16:40:03Z

3

When you spot the duplicate, you need to 'remove' it. You should probably move the last item in the list to the current spot (a[j]) and then decrement dim.

You'll need to consider how the possibly modified dimension is returned to the calling code, but then you also have an issue with how does other code get at the array that's local to the function.

answered Jul 25, 2013 at 16:40

Jonathan Leffler

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Comments

Jiminion · Accepted Answer · 2013-07-25 16:34:38Z

-1

You are moving the number before it is checked. That's why you are missing it. I suggest sorting them first and then check for duplicates later (current == prev). Maybe other techniques would work too.

answered Jul 25, 2013 at 16:34

Jiminion

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