You can give parameters default values. If the caller doesn't provide an argument, the function uses the default: int power(int base, int exponent = 2). Call power(5) and exponent defaults to 2.
Defaults go on the right. int foo(int a = 1, int b) is illegal. The compiler can't tell if you skipped a or b. Defaults must come last. This is useful for common cases. Instead of power(x, 2) everywhere, write power(x) and specify exponent only when it's not 2.