1. FUNCTIONS - What Is A Function? - Advantages Function Declaration
Function Definition
Variable scope
Function Arguments
Passing Arguments by value
Passing Arguments by Reference
Calling other Functions / Recursive

2. What is a Function?
It is a section of code that is enclosed and that provides specific functionality to a program. i.e. - it is enclosed outside the main program - therefore it is called from outside the main program or other functions to provide a service / functionality

3. What is a Function? 3 Main Advantages
Code Easier :- They make the program code easier to understand and to maintain
Code Reuse :Tried and tested function can be reused by other programs
Division of labour : several programmers can divide the workload in a large project by working on different functions for the program

4. What is a Function? Function Declaration
functions must be declared early in the program code, just as it is done for primitive variables
It is declared as a prototype

5. What is a Function? Declaration syntax
return-data-type function-name (arguments-list)
Where return-data-type can be
int
string
char
double
void
among others

6. What is a Function?
where arguments-list - are values to be passed as arguments from the caller - and these can be of any quantity and data type - they must agree with those specified in the prototype function declaration

7. What is a Function? Function Prototype declaration Eg void calcsum();
int calcmean();
double calcstdev();

8. What is a Function?
void calcsum(); declares a function named calcsum(); that accepts no argument -- () is empty and returns no value : because type is void

9. What is a Function? Definition - Appears later in the program code
Comprises a repeat of the prototype together with the function body
where the function body is a pair of braces { }
surrounding the statements that are to be executed when the function is called.

10. Examples
#Include<iostream> using namespace std; //declare the function prototype early void calcsum(); void writetitle(); int sum; int main() { writetitle(); // function calls from main rsum = calcsum(); cout << “The Sum is = “ << rsum << endl ; system(“pause”); return 0; }

11. // function definition
//define the function writetitle() void writetitle() { string dept = “Computer Science”; cout << dept << endl; }

12. // function definition
//define the function calcsum() void calcsum() { int val1 = 20; int val2 = 35; int tot = val1 + val2; cout << “The sum is = “ << tot endln; }

13. Passing values to functions
Functions can be passed values
The caller function passes value in the form of arguments to a function that it calls
These can be of any quantity and data type
But they must agree with those specified in the prototype function declaration

14. Functions can return a value
- the function can return a value of any data-type, as long as it is of the type specified in the function prototype

15. // Function arguments
Note the FUNCTION the Caller FUNCTION Int main() { writeline(); calcsum(); }

16. // Function arguments
#Include<iostream> using namespace std; //declare the function prototype early void calcsum(); void writetitle(); int sum; int main() { writetitle(); // function calls from main calcsum(); system(“pause”); return 0; } //define the function writetitle() void writetitle() string dept = “Computer Science”; cout << dept << endl; //define the function calcsum() void calcsum() int val1 = 20; int val2 = 35; int tot = val1 + val2; cout << “The sum is = “ << tot endln; Pfunction.txt

17. // Function passing arguments by value
Note the Function Prototype arguments and the Function definition arguments
// Function Prototype declaration
int getmax(int n1, int n2);
int getnum();

18. // Function passing arguments by value
// function definition
int getnum()
{ int num
cout << “Enter a number”;
cin >> num;
return num; }

19. // Function passing arguments by value
// function definition
int getmax(int n1, int n2) {
return (n1 > n2) ? n1 : n2; }

20. // Function passing arguments by value
#include<iostream> using namespace std; // function declaration prototype int getnum(); int getmax(int n1 , int n2); //main function int main() { int num1 , num2; num1 = getnum(); num2 = getnum(); // determine the maximum of num1 and num2 cout << “Max number : “ << getmax(num1, num2) << endl; }

21. // Function passing arguments by value
int getnum() { int num cout << “Enter a number”; cin >> num; return num; }

22. // Function passing arguments by value
// function definition
int getmax(int n1, int n2) {
return (n1 > n2) ? n1 : n2; }

23. // Function passing arguments by value
when arguments are passed to a function
it is the value that is passed, not the variable itself