Store some elements of an array in another array

Question

I have defined a array integer in which it will be pointed by a pointer and then I have another array which will store only a few numbers in which are even numbers, here is the code...

void main(void) {

    srand(time(NULL));
    //vetor de dimensao 10
    int vetor [MAX] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    //apontador para vetor
    int *ptr_vetor;
    //novo vetor
    int novo_vetor[MAX];
    //apontador para novo vetor
    int *ptr_novo_vetor;
    //escolher numero
    int escolha = 0;
    //contador
    int contador = 0;

    //ponteiro apontado ao primeiro vetor
    ptr_vetor = &vetor[0];
}

shows the values of the vector

printf("\n--- Vetor ---");
    for (int i = 0; i < MAX; i++) {
        //mostra os valores do vetor
        printf("\nvalor : %d ", vetor[i]);
    }

shows even values pointing to the vector

printf("\n\n--- Ponteiro Vetor para Numero Pares ---");
    for (int i = 0; i < MAX; i++) {
        //escolha apenas numeros pares
        if (*(ptr_vetor + i) % 2 == 0) {
            //mostra os valores pares apontador ao vetor
            printf("\nNumero Par : %d ", *(ptr_vetor + i));
            //adiciona o numero par ao novo vetor
            novo_vetor[i] = *(ptr_vetor + i);
            //aqui devia receber apenas os dados do novo vetor mas
            //mostra aepnas o endereço
            ptr_novo_vetor = &novo_vetor[i];
            //usei isto para iterar os jogadores, nao deu certo
            //contador++;
        }
    }

shows the values of the new vector

printf("\n\n\n--- Novo Vetor ---");
    for (int i = 0; i < MAX; i++) {
        //mostra os valores do novo vetor
        printf("\nvalor: %d ", novo_vetor[i]);
    }

shows the values of the new pointer

printf("\n\n--- Ponteiro Novo Vetor ---");
    for (int i = 0; i < MAX; i++) {
        //mostra os valores do novo ponteiro
        printf("\nNovo Vetor : %d ", *(ptr_novo_vetor+i));
    }

when running the program

How to show the data that has been added to the new array, that is, even numbers?

Answer 1

I’ll give you a solution that I don’t know if it’s what you want. But the code doesn’t make much sense either, so I don’t know if it’ll make a difference. You probably want to do something else and are far from the goal. I am answering for what you have given to understand.

Surely you have better ways of doing this, but I haven’t spent much time thinking about what to improve, because I see no reason for this whole code to exist.

#include <stdio.h>
#define MAX 10

int main(void) {

    //vetor de dimensao 10
    int vetor [MAX] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    //apontador para vetor
    int *ptr_vetor;
    //novo vetor
    int novo_vetor[MAX];
    //apontador para novo vetor
    int *ptr_novo_vetor;
    //escolher numero
//    int escolha = 0;
    //contador
//    int contador = 0;

    //ponteiro apontado ao primeiro vetor
    ptr_vetor = &vetor[0];

    printf("\n--- Vetor ---");
    for (int i = 0; i < MAX; i++) {
        //mostra os valores do vetor
        printf("\nvalor : %d ", vetor[i]);
    }
    
    printf("\n\n--- Ponteiro Vetor para Numero Pares ---");
    for (int i = 0; i < MAX; i++) {
        //escolha apenas numeros pares
        if (*(ptr_vetor + i) % 2 == 0) {
            //mostra os valores pares apontador ao vetor
            printf("\nNumero Par : %d ", *(ptr_vetor + i));
            //adiciona o numero par ao novo vetor
            novo_vetor[i / 2] = *(ptr_vetor + i);
        }
    }
    ptr_novo_vetor = novo_vetor;

    printf("\n\n\n--- Novo Vetor ---");
    for (int i = 0; i < MAX / 2; i++) {
        //mostra os valores do novo vetor
        printf("\nvalor: %d ", novo_vetor[i]);
    }

    printf("\n\n--- Ponteiro Novo Vetor ---");
    for (int i = 0; i < MAX / 2; i++) {
        //mostra os valores do novo ponteiro
        printf("\nNovo Vetor : %d ", *(ptr_novo_vetor+i));
    }
    return 0;
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

Answer 2

Its resulting vector has the wrong size. If it has to receive only even numbers, it cannot be the same size as the original vector. If you do this, you will have to fill the resulting vector with values that indicate empty. Better would be you, already knowing the input set, simply create a vector of 5 positions.

The reason you are skipping positions in the insert is that you are inserting when i is pair and placing in position i. Thus, only even positions will be filled.

Already the ptr_novo_vetor is showing these weird values because you never made him point anywhere.