Arrays and scanf issues; values to use with scanf

Question

This is a simple program to compute ages of people in the room. I am at the very initial stage, and now I see that I do not know which variables (I mean variables that I declare before scanf and then placeholders within scanf) to use for scanf; how to choose and apply a correct variable. Is there a resource that could explain in plain English these issues? Here is the program:

// Ages people by a year. Arrays

#include <stdio.h>

int main (void)
{
    // determine number of people
    int n;
    do
    {
        printf("Number of people in room: ");
        scanf ("%i", &n);
    }
    while (n<1); // get the number of people in the room, pass through user
                 // again and again until the user gives a positive integer

    // declare array in which to store everyone's age

    int ages[n];
    int  i;


    for (i = 0; i < n; i++)
    {
        printf("Age of person #%i: ", i + 1); // person number 1, person number 2, etc
        scanf ("%d", ages[i]); // store the age in the i-th part of the array ages
    }

    // report everyone's age a year hence
    printf("Time passes...\n\n");

    for (i = 0; i < n; i++)
    {
        printf(" A year from now person #%i will be %i years old.\n", i + 1, ages[i] + 1); 
        // we add 1 year to previous age

    }
 }

Answer 1

scanf("%d") expects an address as an argument. Therefore, replace

scanf ("%d", ages[i]);

with

scanf ("%d", ages + i);

(or &ages[i] but that's personal preference.)

Answer 2

scanf expects pointer to some variable in order to change it's value - otherwise it will get some copy that won't affect the real variable.

this line : scanf ("%d", ages[i]); dereference ages and returns an integer, not a pointer to an integer. change it to be scanf ("%d", &ages[i]); the & will extract the memory address of ages[i] and pass it as a pointer to scanf