Can I declare variables of different types in the initialization of a for loop? [duplicate]

Yes, that is prohibited. Just as otherwise you cannot declare variables of differing types in one declaration statement (edit: modulo the declarator modifiers that @MrLister mentions). You can declare structs

for (struct { int a = 0; short b = 0; } d; d.a < 10; ++d.a, ++d.b ) {}

C++03 code:

for (struct { int a; short b; } d = { 0, 0 }; d.a < 10; ++d.a, ++d.b ) {}

Of course when all are 0, you can omit the initializers altogether and write = { }.

Nothing to do with the for loop. This also doesn't compile if you write int a = 0, short b = 0; outside of any loop.
So the answer is: it is always forbidden to declare two variables of different types in a single statement.

Edit: Oh, for the pedantic, I do realise that you can declare a base type and a pointer type in the same statement, for instance an int and an int pointer, so those would be different types, yes.
Hm, that makes me think. In a 32 bit environment, a pointer would be 4 bytes, just like an int, so you could use short a = 0, *b = 0; and then cast b to an int. Hm...

What is prohibited is the ending of a statement with a comma as you do in int a = 0, short ...

If you want to use this notation then bothe variable muss have the same type int i = 0, s = 0;