C - delete element from array and reorganise

Question

Given this array:

int a[] = {5, 8, 5, 6, 9, 5};

Would it be possible to remove all ints which equals 5 and move the rest the front of the array?

So that after the removal the array would look like this:

int a[] = {8, 6, 9, 0, 0, 0}

I don't know if by removing a element it becomes a 0 or a NULL?

Thanks!

You can't make an `int` become a "null" value, it has to be an integer (and `NULL` *is* `0` on most platforms) — UnholySheep, Mar 16 '19 at 09:58
Alright, so that's 1 question answered, what about the main question? — MrEmper, Mar 16 '19 at 09:59
The answer to the main question is: Yes. What have you tried doing? Show the code and explain what issues you have with it — UnholySheep, Mar 16 '19 at 10:00
I haven't, because I can't get my head around the theory. Before I do I want to truly understand whats happening and why. — MrEmper, Mar 16 '19 at 10:01
What _really_ happens is that you have to move down all higher elements to overwrite the value to be deleted and set the appropriate higher element to zero. — Paul Ogilvie, Mar 16 '19 at 10:04
Possible duplicate of [Remove an array element and shift the remaining ones](https://stackoverflow.com/questions/879603/remove-an-array-element-and-shift-the-remaining-ones) — BattleTested_закалённый в бою, Mar 16 '19 at 10:06

score 2 · Answer 1 · answered Mar 16 '19 at 10:56

You can do it with two iterations over the array, first iteration two to turn the element you want to delete, second iteration to separate zeros from non-zeros.

    int a[] = {5, 8, 5, 6, 9, 5};
    int n = 6;
    for(int i = 0 ; i < n ; i++ ) {
        if(a[i] == 5 ) {
            a[i] = 0;
        }
    }
    int* zero = a;

    int* nonZero = a;
    int j = 0;

    while(j < n) {

        while(*zero != 0) {
            zero++;
        }       

        while(*nonZero == 0) {
            nonZero++;
            j++;
        }
        if(zero < nonZero) {
            *zero = *nonZero;
            *nonZero = 0;
        }
        j++;
    }

BattleTested_закалённый в бою · Accepted Answer · 2019-03-16T10:10:20.553

1

Your array is statically allocated, so always has the same size and deleted elements have the 0 value (according how you define the deleted values).

This link can help you and explains about how to delete element from array.

edited Mar 16 '19 at 10:10

answered Mar 16 '19 at 10:04

BattleTested_закалённый в бою

4,037
5
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score 0 · Answer 3 · 2019-03-16T10:22:14.260

0

It is been awhile that i have programmed in C but it is posibble.

This is just a pseudo code, but you just need to change it to way of C programming.

int a[] = {5, 8, 5, 6, 9, 5};
int b[] = {5, 8, 5, 6, 9, 5}; // copy of array a to hold temp
for(int i = 0; i < Size of array; i++ ){
  for(int j = i; j < Size of array; j++ ){
    if(b[j] != 5){
       a[i] = b[j];
       a[j] = b[i];
       break;
    }
  }
}

It will be like (▼: Target to swap, F: Finished, X: Not a targe to swap, N: Not processed):

▼, ▼, N, N, N, N

5, 8, 5, 6, 9, 5

F, ▼, X, ▼, N, N

8, 5, 5, 6, 9, 5

F, F, ▼, X, ▼, N

8, 6, 5, 5, 9, 5

Result: 8, 6, 9, 5, 5, 5

And remove 5s, it is quite different depends what you mean. If you do not change size of array then they can be 0 or undefined(null). So I think it differs by how you program the function that returns array.

edited Mar 16 '19 at 10:22

answered Mar 16 '19 at 10:16

2

That is super inefficient in both space and time usage. Also how do you change the size of a statically sized array? That's not possible in standard C – UnholySheep Mar 16 '19 at 10:24
As far as I remember, he did not ask for performance. Well if you are that much experienced, what about you edit/write answer for everyone! :) And true, it is impossible to change statically sized array but if you create new array with diffrent size but having only numbers without 5s yes that work. So that is matter of how you program things in my opinion. Once again, we are not focusing on high performance optimization here. – Mar 16 '19 at 11:30

score 0 · Answer 4 · answered Mar 16 '19 at 10:23

0

your array is not dynamic so you just can't reduce its size after its been allocated.setting the value zero might solve the problem in your case.

answered Mar 16 '19 at 10:23

2

That is not what OP asked - nowhere in their question do they ask about reducing the size of the array – UnholySheep Mar 16 '19 at 10:24

C - delete element from array and reorganise

4 Answers4