Counter adding an extra value to the vector with pointer

Question

I’m trying to finish an exercise that asks for 4 ages and the output tells how many of the inserted ages are greater than or equal to 18 but the counter always adds a value greater than 18 at the end and I don’t understand why.

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

int main()
{
int vetor[3], *pvetor = &vetor[0],i,cont=0;
for(i=0;i<4;i++)
{
    printf("Introduza a %d idade: ",i+1);
    scanf("%d",&vetor[i]);
}
while(*pvetor != NULL)
{
    if(*pvetor >= 18)
        cont++;
    pvetor++;
}
printf("Das %d idades inseridas, %d sao maiores de idade.",4,cont);
}

Answer 1

If it is to receive 4 ages o array should have size 4. You can count already on the input. No need for pointer. If you know it is 4 ages you have no reason to parameterize this. And this is C, not C++.

#include <stdio.h>

int main() {
    int vetor[4], cont=0;
    for (int i = 0; i < 4; i++) {
        printf("Introduza a %da. idade: ", i + 1);
        scanf("%d", &vetor[i]);
        if (vetor[i] >= 18) cont++;
    }
    printf("Das 4 idades inseridas, %d sao maiores de idade.", cont);
}

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