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C++ Chapter IV
The document provides an overview of functions in C++. It defines what a function is, its typical components like name, parameters, return type and statements. It gives examples of calling functions by value and by reference. It also discusses the differences between global and local scope, and how variables declared inside and outside functions are accessed. The objective is to teach how to define, prototype and call functions as well as understand their scope.
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C++ Chapter IV
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- 2. Objec9ve A=er completely this chapter, you will be able to: • Define func9on • Define Scope role • Construct func9on headers and prototypes • Call by value and Call by reference • Define storage class specifiers Lecturer: Hong Mom 2
- 3. Func9on • What is Func9on? A func&on is a block of code that performs a calcula9on and returns a value. Once a func9on has been wriNen to play a par9cular role it can be called upon repeatedly throughout the program. • Also called a subrou&ne, procedure, or method Lecturer: Hong Mom 3
- 4. Func9on • Func9on is normally consist these factors as below Name Parameters Statements Type type name (parameter1, paramter2,…) { statements; } Lecturer: Hong Mom 4
- 5. Func9on • type is the data type specifier of the data returned by the func9on. • name is the iden9fier by which it will be possible to call the func9on. • parameters (as many as needed): Each parameter consists of a data type specifier followed by an iden9fier, like any regular variable declara9on Lecturer: Hong Mom 5
- 6. Func9on (for example: int x) and which acts within the func9on as a regular local variable. They allow to pass arguments to the func9on when it is called. The different parameters are separated by commas. • statements is the func9on's body. It is a block of statements surrounded by braces { }. Lecturer: Hong Mom 6
- 7. Example1 #include<iostream.h> int sum2Num(int a, int b) { The result is 13 int s; s = a + b; return (s); } int main(){ int r; r = sum2Num(5,8); cout << “The result is “ << r; return 0; } Lecturer: Hong Mom 7
- 8. Example2 • Way1 Output: #include <iostream.h> void displayNum(int num) { num = 0; num = 0; x = 10; cout << "num = " << num << 'n'; } int main (void) { int x = 10; displayNum (x); cout << "x = " << x << 'n'; return 0; } Lecturer: Hong Mom 8
- 9. Example2 • Way2 #include <iostream.h> void displayNum(int num); //Func9on Declara9on or Prototype int main (void) { int x = 10; displayNum (x); cout << "x = " << x << 'n'; return 0; } void displayNum(int num) { num = 0; cout << "num = " << num << 'n'; } Lecturer: Hong Mom 9
- 10. Global and Local Scope • Global Scope -‐ Everything defined at the program scope level (i.e., outside func9ons and classes) is said to have a global scope -‐ Can be accessed by any func9on defined below the declara9on • Local Scope -‐ Each block in a program defines a local scope . -‐ In general variables declared inside a block are accessible only in that block Lecturer: Hong Mom 10
- 11. Scope of variables #include <iosteam.h> int x; char ch; Global variables main() { int age; Local variables float number; cout << “Enter your age: “; cin >> age; … } Lecturer: Hong Mom 11
- 12. Call of Func9on Func&on Call by value Func&on Call by Reference #include <iostream.h> #include <iostream.h> #include<iostream.h> #include<iostream.h> void swap(int x, int y){ void swap(int &x, int &y){ int temp = x; int temp = x; x = y; x = y; y = temp; y = temp; } } Lecturer: Hong Mom 12
- 13. Call of Func9on void main() { int a = 10; int b = 20; swap(a, b); cout<<”a: ” << a<<” and b: ” <<b; } Func&on Call by value a:10 and b: 20 Func&on Call by Reference a:20 and b: 10 Lecturer: Hong Mom 13
- 14. Storage class specifiers • A storage class specifier is used to refine the declara9on of a variable in memory. • The storage class specifiers in C++ are: – Auto – Register – Sta9c – Extern Lecturer: Hong Mom 14
- 15. Auto Variables Because the life9me of a local variable is limited and is determined automa9cally, these variables are also called automa&c. The storage class specifier auto may be used to explicitly specify a local variable to be automa9c. For example: void showMe(void) { auto int xyz; // same as: int xyz; //... } This is rarely used because all local variables are by default automa9c. Lecturer: Hong Mom 15
- 16. Register variable • Used to indicate to the compiler that the variable should be stored in a register if possible. • The scope of register variables is local to the block in which they are declared. • fast For example: register int var; Lecturer: Hong Mom 16
- 17. Sta9c variable • Preserve the value for a par9cular variable upon re-‐entry into the same func9on. For example: void sta9c_func9on_example() { sta9c int x = 0; //variable for C++ tutorial example x++; cout << x <<endl; } Lecturer: Hong Mom 17
- 18. Extern variable • Used to specify that the variable is declared in a different file. • Used to declare variables of global scope in C+ + projects • When the keyword extern is used, the compiler will not allocate memory for the variable. Lecturer: Hong Mom 18