Array prints all positions correctly, except 8, 9, 10

I’m trying to implement Array ADT in C:

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

#define sizeArr 20

struct array{

int* A;
int size; //size is the actual size of A
int length; //length are the positions actually being used in A,from A[0] to A[length-1]

};

void fillArray( struct array* arr ){

    printf( "Number of elements in array (max. %i): ", arr->size );
    scanf( "%i", &arr->length );

    if( arr->length <= arr->size ){

        for ( int i = 0; i < arr->length; i++ ){
    
            printf( "arr[%i] := ", i );
            scanf( "%i", &arr->A[i] );

        }

    }else
        exit(1);

}

void displayArray( struct array* arr ){

    for ( int i = 0; i < arr->length; i++ )
        printf( "%i\n", arr->A[i] );

}

void appendArray( struct array* arr, int element ){

    if( arr->length < arr->size )
        arr->A[arr->length++] = element;
    else
        exit(1);

}

int main( void ){

struct array arr = { .size = sizeArr, .A = ( int* ) malloc( arr.size*sizeof(int) ), .length = 0 };

fillArray( &arr );
printf("%i", arr.size);
displayArray( &arr );
appendArray( &arr, 41 );
printf("--------\n");
displayArray( &arr );

free( arr.A );
return 0;

}

When I choose arr.length = 7 I get this; works properly.

When I choose arr.length = 8 I get this; You can see that instead of appending 41, it does so with some other random number, probably garbage.

When I choose arr.length = 16 I get this; You can appreciate that 41 is succesfully apended, but positions 8, 9, 10, exclusively, print garbage instead of the values they were asigned; all other array positions are printed properly.

I’ve been wrapping my head around this for a few hours, however I don’t know whats wrong with the code; the only problems that I think could lead to this are:

• arr.A is not actually being given arr.size as its size.

• displayArray() is priting this positions wrongly, but the correct numbers are there

• appendArray() and fillArray() have some kind of issue whe inserting elements in this positions.

If y’all could help me sorting out this issue, I’d really appreciate it.

Thanks in Advance.

>Solution :

You cannot refer to a previous member of a struct within the initialization. Use sizeArr instead:

    struct array arr = {
        malloc(sizeArr*sizeof(int)),
        sizeArr,
        0
    };

Or even better write a function to create an array. malloc() may fail so it’s a good idea to implement error checks.