When a function has a specific-size array parameter, why is it replaced with a pointer?

Given the following program,

#include <iostream>

using namespace std;

void foo( char a[100] )
{
    cout << "foo() " << sizeof( a ) << endl;
}

int main()
{
    char bar[100] = { 0 };
    cout << "main() " << sizeof( bar ) << endl;
    foo( bar );
    return 0;
}

outputs

main() 100
foo() 4

1. Why is the array passed as a pointer to the first element?
2. Is it a heritage from C?
3. What does the standard say?
4. Why is the strict type-safety of C++ dropped?