Strange behavior when reading and writing "float" and "double" types in C

Question

When I put 1 for example this return 1.000 (that's fine to me):

#include <stdio.h>

main()
{
    float num;

    printf("Double: ");
    scanf("%f", &num);

    printf("%f\n", num);
}

So, when I put 1 at this it returns 0.000. I don't understand because I used %f to read and write correctly. Can you guys explain me?

#include <stdio.h>

main()
{
    double num;

    printf("Double: ");
    scanf("%f", &num);

    printf("%f\n", num);
}