Remove even numbers from array in c

问题:

Hello i'm trying for about 2 hours to create a program which will remove even numbers from a dinamyc allocated array(with malloc)in c.Can somebody help me with some tips or create the code.

p.s. this is my first topic here, so feel free to give me some tips about how to correctly post a qustion.

回答1:

Let's assume that you already allocated dynamically an array of n elements and initialized it.

In this case the function that removes elements with even values can look the following way

size_t remove_even( int *a, size_t n )
{
    size_t m = 0;

    for ( size_t i = 0; i < n; i++ )
    {
        if ( a[i] % 2 != 0 )
        {
            if ( i != m ) a[m] = a[i];
            ++m;
        }
    }

    return m;
}

It can be called the following way

size_t m = remove_even( p, n );

for ( size_t i = 0; i < m; i++ ) printf( "%d ", a[i] );
printf( "\n" );

where p is the pointer to your dynamically allocated array of n elements.

The function actually removes nothing. It simply moves odd elements to the beginning of the array.

You can then use standard C function realloc to delete physically the removed elements.

For example

int *tmp = realloc( p, m * sizeof( int ) );

if ( tmp != NULL ) p = tmp;

Here is a demonstrative program

#include <stdlib.h>
#include <stdio.h>

size_t remove_even( int a[], size_t n )
{
    size_t m = 0;

    for ( size_t i = 0; i < n; i++ )
    {
        if ( a[i] % 2 != 0 )
        {
            if ( i != m ) a[m] = a[i];
            ++m;
        }
    }

    return m;
}

#define N   10

int main( void )
{
    int *a = malloc( N * sizeof( int ) );

    for ( size_t i = 0; i < N; i++ ) a[i] = i;

    for ( size_t i = 0; i < N; i++ ) printf( "%d ", a[i] );
    printf( "\n" );

    size_t m = remove_even( a, N );

    int *tmp = realloc( a, m * sizeof( int ) );

    if ( tmp != NULL ) a = tmp;

    for ( size_t i = 0; i < m; i++ ) printf( "%d ", a[i] );
    printf( "\n" );

    free( a );
}

Its output is

0 1 2 3 4 5 6 7 8 9 
1 3 5 7 9 

回答2:

There are some things which you need to check before you try to code something, but I see that there is no code which you showed use.

SO is not a tutorial site, so this means that you should show us some code which actually does compile and ask here if there are some problems with that code.

Any way until than, this code should give you an Idea about how to check if a Number is odd or even:

#include<stdio.h>
#include<stdlib.h>

int main(void){
    int n;

    printf("Enter an integer:>  ");
    if((scanf("%d", &n)) != 1){
        printf("Error, Fix it!\n");
        exit(1);
    }

    if (n%2 == 0){
        printf("Even\n");
    }else{
        printf("Odd\n");
    }

    return 0;
}

The whole story here is not about checking if Numbers inside an Array are odd or even, is about to find a way to check if a number is odd or even and only then you should check if inside that array there are odd or even numbers. I hope you understand my point.