why showing this error in codeblocks?

Question

||=== Build: Debug in Composition (compiler: GNU GCC Compiler) ===|
C:\Users\noman\Desktop\My C++ codes for learning\Composition\Birthday.cpp|3|error: redefinition of 'Birthday::Birthday(int, int, int)'|
C:\Users\noman\Desktop\My C++ codes for learning\Composition\Birthday.h|9|note: 'Birthday::Birthday(int, int, int)' previously defined here|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

Answer 1

It says that you're re-defining the definition of a constructor. You could be doing this.

class A() {
public:
A(int m, int d, int y);
};
A::A(int m, int d, int y) {
// some code
}

// here your redefining it again
// this is causing the error.
A::A(int m, int d, int y) {
// some code
}

if you're trying to overload then you should remember that there has to be a change in the type of params or in the number of params. or the methods be declared as constant and non-constant.