Is it explicit or implicit type conversion?

Question

When a format specifier of a type that is different from the variable is used with printf to show a value of another data type then it's implicit type conversion or explicit one?

#include <stdio.h>

int main()
{
    double a = 3.5;
    int b = 6;

    printf("Value of a as int: %d\n", a);
    printf("Value of b as double: %lf", b);

    return 0;
}

Output:

Value of a as int: 0

Value of b as double: 3.500000

I also want to know why the value of a is printed instead of b?