1. CSC1201: Programming Language 2
Functions I

2. – Organize code in program – Code are easier to maintain?
A Function is a group of statements that together perform a task. It can be used anywhere in the program. Why we need function?
– Organize code in program
– Code are easier to maintain?
Function declaration: return_type FuncName(Type arg1, Type arg2,….. Type argN) { function body }
A program can contain one or many functions
Must always have a function called “main”.
The main function is the starting point of all C++ programs
The compiler will not compile the code unless it finds a function called “main” within the program.

3. “Hello World” program
#include <iostream> using namespace std; int main ()‏ { cout << “Hello World\n”; Return 0; }

4. Function
When we need function? – When you need to repeat the same process over and over in a program. – The function can be called many times but appears in the code once.

5. 1- Predefined functions
Predefined functions are functions that are built into C++ Language to perform some standard operations.
The C++ standard library provides numerous built-in functions that your program can call. For example, function strcat() to concatenate two strings
the definitions have been written and it is ready to be used.
– User needs to include pre-defined header file (i.e. math.h, time.h)

6. 2- User defined functions
Function that been created by the user.
– This functions need to be declared and defined by the user

7. functions Value returning functions: Void functions:
functions that have a return type.
These functions return a value of a specific data type using the return statement.
Void functions:
functions that do not have a return type.
These functions do not use a return statement to return a value.

8. Value returning functions
The syntax is:
FuncType FuncName(formal parameter list )‏ {
statements }

9. Void functions The syntax is: Void FuncName ( formal parameter list )‏{
statements }

10. Examples:
Write a Function larger, which returns the larger of the two given integers.
Write a Function Square, which returns the square of the given integer.
Write a function number_type. The function should output the number and message saying whether the number is positive, negative, or zero.

11. Example: With return value
Double larger ( double x , double y )‏ { double max; if ( x >= y )‏ max = x; else max = y; return max; } Function Call …….. Cout << “The larger of 5 and 6 is “ << larger(5 , 6) << endl; ……….
Solution Ex 1

12. Example: With return value
#include<iostream> using std::cin; using std::cout; using std::endl; int square (int x)‏ { return x*x; } int main ( )‏ int number; cout<<"Enter any number to Calculate the square of this number "; cin>>number; cout<<endl; cout<<"the square of "<<number<<" is " <<square(number)<<endl; return 0;
Solution Ex 2

13. Example: Without return value
Void number_type ( int x)‏ { if ( x > 0 )‏ cout << x << “ is positive.” << endl; else if ( x < 0 )‏ cout << x << “ is negative.” << endl; else cout<< x << “is a zero.”<<endl; } Function Call …….. Number_type( 5 ); ……….
Solution Ex 3