When a program calls a function, program control is transferred to the called function. A called function performs defined task and when it's return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program.
Based on the parameters and return values, functions can be categorized into four types. They are:
1. Function without arguments and without return value.
2. Function without arguments and with return value.
3. Function with arguments and with return value.
4. Function with arguments and without return value.
