How much of C++ applies to C?

If your project is restricted to ANSI C, knowing C++ won't help you unless you also know where C and C++ overlap. The C compiler will complain for things otherwise valid in C++.

Some of the more obvious differences:

1. no bool (depends on compiler)
2. no classes
3. no member functions
4. local variables must be declared at the start of function scope.

Take the for loop, for example.

This is okay in C++:

for (int i = 0; i < 10; i++)

ANSI C expects this:

int i;
for (i = 0; i < 10; i++)

You might be better off learning C first. There's less to learn. Everything will carry forward when you learn C++ - and you'll know the differences.

C++ is a superset of the C language. Originally Bjarne Stroustrup created C++ as a way to add classes to C. And as such, C++ was born.

So if you know C++ you know C.