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Object Oriented

Programming using C++

Lecture – 5

Functions

Functions

„ Functions or sub- routines are a set of instructions / statements which can be grouped into units „ It helps reducing the program size, and improves program organization

//function //call func(); . . . //function //call func(); .

func() {

..... }

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Function Components

Component Purpose Example

Declaration (prototype)

Specifies the function name, its arguments, and return value types. Declaration alerts the compiler that the function is coming later

int square(int a);

Call Causes the function to be executed

int y = square(2);

Function definition

Body of function int square(int a) { return a*a; }

Function Arguments

„ Function can be called by passing constant values in arguments E.g., void function (char a, int b); //declaration And the function call can be function(+, 24); „ Similarly the function call can be invoked by passing values as arguments char c = +; int x = 24; function(c, x); „ In both cases, the function will create new variables, and the values passed by the function call will be assigned to them

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Reference Arguments

„ Arguments can be passed by Reference in a function call E.g., void add(int, int, int&); int a, b, sum; add(a, b, sum); cout<<sum; void add(int a1, int b1, int& sum1) { sum1 = a1 + b1; }

„ In reference passing the memory address of the variable is passed to the function call „ It is similar as passing a pointer to the variable address

Reference Vs. Pointers

„ A reference parameter is a constant pointer , i.e., after initializing this parameter, it can’t be changed int a = 20; int& Ref; Ref = a;

Ref += 20;

cout<<Ref; cout<<a;

40 40

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Reference Vs. Pointers (contd..)

int b = 30; Ref = b;

Ref += 20; b -= 30;

cout<<Ref; cout<<a; cout<<b;

50 50 0

• Ref is an alias of int a.
• Once it is initialized, it will only work with a.
• When we assigned Ref = b, only the value of b will be assigned.
• This means the value of a has also changed.
• However, nothing will happen to b, and will be treated as an independent variable.

Reference Vs. Pointers (contd..)

„ A pointer is variable which stores the address of a memory location „ It can be assigned address of any variable of the same data type for which the pointer is defined

int a = 0; int* ptr = &a;

*(ptr) += 30; a += 30;

cout<<a; cout<<*(ptr);

60 60

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Reference Vs. Pointers (contd..)

int b = 0; int* ptr = &b;

b = 20; *(ptr) += 30;

cout<<b; cout<<*(ptr); cout<<a;

50 50 60

• Pointer is variable to store memory address.
• It can be changed any time during the program to point at an address of different variable. (Unlike Reference)

Function Return

„ Computed values or data can be returned from a function using the return statement

float power(float number, int power) { float result = 1; for(int i = 0; i < power; i++) result *= number; return number; }

„ Similarly you can return different data types and structures using the return statement

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Overloaded Functions

„ Functions can be overloaded to perform different operations, depending upon the function call „ Overloading can be done using different number of arguments, or even different types of arguments

‰ E.g., ‰ void function(); ‰ void function(int a); ‰ void function(int a, int b); ‰ void function(float a, float b);

Overloaded Functions (contd..)

void function() { cout<<“this function has no argument”; }

void function(int a) { cout<<“this function has an integer argument :”<<a; }

void function(int a, int b) { cout<<“this function has two integer arguments :”<<a<<“ and ”<<b; }

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Inline Functions

„ Used to save the execution time, e.g., in time critical applications you may require to avoid frequent jumps to the function body „ Writing inline in the function declaration/definition tells the compiler to add the code into the main() function of the program at each call ‰ E.g., ‰ inline void function(int, float);

Storage types

„ So far the data types (variables) have been declared/defined as external or automatic (internal) ‰ External: „ At the top (under #include statements), and visible to all the code which follow ‰ Automatic/Internal: „ In a function body, and visible to the code in the function body only „ What happen if you try to access an automatic variable outside the function body? „ ERROR!

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Storage types (contd..)

„ Static variables ‰ Visible inside a function body only, same as automatic variable ‰ However, lifetime is for the whole program, i.e., they retain their values even after the function call has ended (unlike automatic variables). ‰ E.g., „ static int a = 12;

Storage types (contd..)

Automatic / Internal

External Static

Visibility Function body Whole program

Function body

Lifetime Function body Whole program

Whole program Initial Value

Not initialized, arbitrary value

0 0

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Arrays

„ Arrays are used to group the data of similar types, e.g., an array of int, or an array of structures E.g., int arr[10]; //an array of 10 integers

struct shape { int length; int width; int height; }; shape box[200]; //an array of 200 boxes

Arrays (contd..)

„ Arrays are processed by accessing individual elements E.g., cin>>arr[5];//setting the value of 5 th^ element Or cout<<(box[20].lengthbox[20].widthbox[20].height); //displaying the volume of 20 th^ box

„ Arrays can be initialized at declaration/definition int arr[5] = {12, 32, 78, 1, 22};

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Arrays (contd..)

„ Arrays can be multi- dimensional E.g., shape Box[3][3] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

Multi-dimensional arrays are stored sequentially in the memory

Box[0][0]

1 2 3 4 5 6 7 8 9

Box[0][1] Box[0][2] Box[1][0] Box[1][1] Box[1][2] Box[2][0] Box[2][1] Box[2][2]

Box[3][3]

C-Strings

„ A string is an array of characters ‰ E.g., ‰ char str[100]; //An array of 100 characters ‰ cin>>str; //Input using cin ‰ cout<<“The input is : ”<<str; //output

„ String arrays must end with a null character , i.e., \0 „ The operator >> considers “space” to be a terminating character at the console input

C-Strings (contd..)

„ You can use cin.get() function to read a complete line containing blanks as well E.g., cin.get(str, maximum-characters); //the function will copy up to maximum //characters //from the console to string “str”

„ To read multiple lines cin.get(str, maximum-characters, ‘terminating- character’); //this will copy up to maximum-characters from console //to string “str”, until the terminating character has been //typed