Method Overloading and Parameter Passing in CS112: An Introduction to Programming | Slides C programming

CS 112 Introduction to

Programming

Lecture #13:

Method Overloading

and Parameter Passing

http://flint.cs.yale.edu/cs112/

Outline

rAdmin. and review

qMore about defining and using methods

¦Method header

¦Overloading and signature

¦Method parameter passing

¦Method body

¦Variable scope and duration

Recap: Methods

rA method should provide a well-defined, easy-to-

understand functionality

mA method takes input (parameters), performs some actions,

and (sometime) returns a value

rWriting a custom method

mHeader

•Properties ReturnType Name( Param1, Param2, … )

mBody

•Contains the code of what the method does

•Contains the return value if necessary

mAll methods must be defined inside of a class

Outline

MaximumValue.cs

1// MaximumValue.cs

2// Finding the maximum of three doubles.

4using System;

6class MaximumValue

7 {

8// main entry point for application

9static void Main( string[] args )

10 {

11 // obtain user input and convert to double

12 Console.Write( "Enter first floating-point value: " );

13 double number1 = Double.Parse( Console.ReadLine() );

15 Console.Write( "Enter second floating-point value: " );

16 double number2 = Double.Parse( Console.ReadLine() );

18 Console.Write( "Enter third floating-point value: " );

19 double number3 = Double.Parse( Console.ReadLine() );

21 // call method Maximum to determine largest value

22 double max = Maximum( number1, number2, number3 );

24 // display maximum value

25 Console.WriteLine("\nmaximum is: " + max );

27 } // end method Main

The program gets three

values from the user

The three values are then passed

to the Maximum method for use

Outline

MaximumValue.cs

Program Output

29 // Maximum method uses method Math.Max to help determine

30 // the maximum value

31 static double Maximum( double x, double y, double z )

32 {

33 return Math.Max( x, Math.Max( y, z ) );

35 } // end method Maximum

37 } // end class MaximumValue

Enter first floating-point value: 37.3

Enter second floating-point value: 99.32

Enter third floating-point value: 27.1928

maximum is: 99.32

The Maximum method receives 3

variables and returns the largest one

The use of Math.Max uses the Max

method in class Math. The dot

operator is used to call it.

The Dual Roles of C# Classes

rProgram modules:

•a list of (static) method declarations and (static) data

fields

•To make a method static, a programmer applies the

static modifier to the method definition

•The result of each invocation of a class method is

completely determined by the actual parameters (and

static fields of the class)

•To use a static method:

ClassName.MethodName(…);

rBlueprints for generating objects:

•Create an object

•Call methods of the object:

objectName.MethodName(…);

Partial preview of the text

Download Method Overloading and Parameter Passing in CS112: An Introduction to Programming and more Slides C programming in PDF only on Docsity!

CS 112 Introduction to

Programming

Lecture #13:

Method Overloading

and Parameter Passing

http://flint.cs.yale.edu/cs112/

Outline

r Admin. and review

q More about defining and using methods

¶ Method header

¶ Overloading and signature

¶ Method parameter passing

¶ Method body

¶ Variable scope and duration

Recap: Methods

r A method should provide a well-defined, easy-to-

understand functionality

m A method takes input (parameters), performs some actions,

and (sometime) returns a value

r Writing a custom method

m Header

Properties ReturnType Name ( Param1 , Param2 , … )

m Body

Contains the code of what the method does
Contains the return value if necessary

m All methods must be defined inside of a class

Outline

MaximumValue.cs

1 // MaximumValue.cs 2 // Finding the maximum of three doubles. 3 4 using System; 5 6 class MaximumValue 7 { 8 // main entry point for application 9 static void Main( string[] args ) 10 { 11 // obtain user input and convert to double 12 Console.Write( "Enter first floating-point value: " ); 13 double number1 = Double.Parse( Console.ReadLine() ); 14 15 Console.Write( "Enter second floating-point value: " ); 16 double number2 = Double.Parse( Console.ReadLine() ); 17 18 Console.Write( "Enter third floating-point value: " ); 19 double number3 = Double.Parse( Console.ReadLine() ); 20 21 // call method Maximum to determine largest value 22 double max = Maximum( number1, number2, number3 ); 23 24 // display maximum value 25 Console.WriteLine("\nmaximum is: " + max ); 26 27 } // end method Main

The program gets three

values from the user

The three values are then passed

to the Maximum method for use

Outline

MaximumValue.cs

Program Output

29 // Maximum method uses method Math.Max to help determine 30 // the maximum value 31 static double Maximum( double x, double y, double z ) 32 { 33 return Math.Max( x, Math.Max( y, z ) ); 34 35 } // end method Maximum 36 37 } // end class MaximumValue

Enter first floating-point value: 37. Enter second floating-point value: 99. Enter third floating-point value: 27.

maximum is: 99.

The Maximum method receives 3

variables and returns the largest one

The use of Math.Max uses the Max

method in class Math. The dot

operator is used to call it.

The Dual Roles of C# Classes

r Program modules:

• a list of (static) method declarations and (static) data

fields

• To make a method static, a programmer applies the

static modifier to the method definition

• The result of each invocation of a class method is

completely determined by the actual parameters (and

static fields of the class)

• To use a static method:

ClassName.MethodName(…);

r Blueprints for generating objects:

• Create an object

• Call methods of the object:

objectName.MethodName(…);

Explicitly Creating Objects

r A class name can be used as a type to

declare an object reference variable

String title;

Random myRandom;

r An object reference variable holds the

address of an object

r No object has been created with the above

declaration

r The object itself must be created using the

new keyword

Creating and Accessing Objects

r We use the new operator to create an object

Random myRandom;

myRandom = new Random();

This calls theThis calls the RandomRandom constructorconstructor , which is, which is

a special method that sets up the objecta special method that sets up the object

r Creating an object is called instantiation

m An object is an instance of a particular class

r To call an ( instance ) method on an object, we

use the variable (not the class), e.g.,

Random generator1 = new Random();

int num = generate1.Next();

Example: the Random class

Random Random ()

Some methods from the Random class

int Next ()

// returns an integer from 0 to Int32.MaxValue

int Next (int max)

// returns an integer from 0 upto but not including max

int Next (int min, int max)

// returns an integer from min upto but not including max

double NextDouble ( )

// returns a double number from 0 to 1

See RandomNumbers.cs

Outline

RandomInt.cs

1 // RandomInt.cs 2 // Random integers. 3 4 using System; 5 using System.Windows.Forms; 6 7 // calculates and displays 20 random integers 8 class RandomInt 9 { 10 // main entry point for application 11 static void Main( string[] args ) 12 { 13 int value; 14 string output = ""; 15 16 Random randomInteger = new Random(); 17 18 // loop 20 times 19 for ( int i = 1; i <= 20; i++ ) 20 { 21 // pick random integer between 1 and 6 22 value = randomInteger.Next( 1, 7 ); 23 output += value + " "; // append value to output 24 25 // if counter divisible by 5, append newline 26 if ( i % 5 == 0 ) 27 output += "\n"; 28 29 } // end for structure 30

Creates a new Random object

Will set value to a random number

from1 up to but not including 7

Format the output to only have

5 numbers per line

Outline

RandomInt.cs

Program Output

31 MessageBox.Show( output, "20 Random Numbers from 1 to 6", 32 MessageBoxButtons.OK, MessageBoxIcon.Information ); 33 34 } // end Main 35 36 } // end class RandomInt

Display the output in a message box

A Quick Summary

r If a method is a static method

m Call the method by

ClassName.MethodName(…);

r If a method of a class is not a static method,

then it is an instance method

m Create an object using the new operator

m Call methods of the object:

objectVariableName.MethodName(…);

r We will study instance methods in more detail

in the future

Recall: Calling a Method

r Each time a method is called, the actual arguments in

the invocation are copied into the formal arguments

static int SquareSum (int num1, int num2)

int sum = num1 + num2;

return sum * sum;

int num = SquareSum (2, 3);

Parameters: Modifying Formal Arguments

r You can use the formal arguments (parameters) as

variables inside the method

r Question: If a formal argument is modified inside a

method, will the actual argument be changed?

static int Square ( int x )

x = x * x;

return x;

static void Main ( string[] args )

int x = 8;

int y = Square( x );

Console.WriteLine ( x );

Parameter Passing

r If a modification on the formal argument has no

effect on the actual argument,

m it is call by value

r If a modification on the formal argument can

change the actual argument,

m it is call by reference

Call-By-Value and Call-By-Reference in C#

r Depend on the type of the formal argument

r For the simple data types, it is call-by-value

r Change to call-by-reference

m The ref keyword and the out keyword change a

parameter to call-by-reference

• If a formal argument is modified in a method, the value is

changed

• The ref or out keyword is required in both method

declaration and method call

• ref requires that the parameter be initialized before

enter a method while out requires that the parameter be

set before return from a method

Example: ref

static void Foo( int p ) {++p;}

static void Main ( string[] args )

int x = 8;

Foo( x ); // a copy of x is made

Console.WriteLine( x );

static void Foo( ref int p ) {++p;}

static void Main ( string[] args )

int x = 8;

Foo( ref x ); // x is ref

Console.WriteLine( x );

} See TestRef.cs

Example: out

static void Split( int timeLate,

out int days,

out int hours,

out minutes )

days = timeLate / 10000;

hours = (timeLate / 100) % 100;

minutes = timeLate % 100;

static void Main ( string[] args )

int d, h, m;

Split( 12345, out d, out h, out m );

Console.WriteLine( “{0}d {1}h {2}m”, d, h, m );

See TestOut.cs

Outline

RefOutTest.cs

1 // RefOutTest.cs 2 // Demonstrating ref and out parameters. 3 4 using System; 5 using System.Windows.Forms; 6 7 class RefOutTest 8 { 9 // x is passed as a ref int (original value will change) 10 static void SquareRef( ref int x ) 11 { 12 x = x * x; 13 } 14 15 // original value can be changed and initialized 16 static void SquareOut( out int x ) 17 { 18 x = 6; 19 x = x * x; 20 } 21 22 // x is passed by value (original value not changed) 23 static void Square( int x ) 24 { 25 x = x * x; 26 } 27 28 static void Main( string[] args ) 29 { 30 // create a new integer value, set it to 5 31 int y = 5; 32 int z; // declare z, but do not initialize it 33

When passing a value by reference

the value will be altered in the rest

of the program as well

Since x is passed as out the variable

can then be initialed in the method

Since not specified, this value is defaulted to being

passed by value. The value of x will not be changed

elsewhere in the program because a duplicate of the

variable is created.

Since the methods are void

they do not need a return value.

Outline

RefOutTest.cs

34 // display original values of y and z 35 string output1 = "The value of y begins as " 36 + y + ", z begins uninitialized.\n\n\n"; 37 38 // values of y and z are passed by value 39 RefOutTest.SquareRef( ref y ); 40 RefOutTest.SquareOut( out z ); 41 42 // display values of y and z after modified by methods 43 // SquareRef and SquareOut 44 string output2 = "After calling SquareRef with y as an " + 45 "argument and SquareOut with z as an argument,\n" + 46 "the values of y and z are:\n\n" + 47 "y: " + y + "\nz: " + z + "\n\n\n"; 48 49 // values of y and z are passed by value 50 RefOutTest.Square( y ); 51 RefOutTest.Square( z ); 52 53 // values of y and z will be same as before because Square 54 // did not modify variables directly 55 string output3 = "After calling Square on both x and y, " + 56 "the values of y and z are:\n\n" + 57 "y: " + y + "\nz: " + z + "\n\n"; 58 59 MessageBox.Show( output1 + output2 + output3, 60 "Using ref and out Parameters", MessageBoxButtons.OK, 61 MessageBoxIcon.Information ); 62 63 } // end method Main 64 65 } // end class RefOutTest

Method Overloading and Parameter Passing in CS112: An Introduction to Programming, Slides of C programming

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Partial preview of the text

Download Method Overloading and Parameter Passing in CS112: An Introduction to Programming and more Slides C programming in PDF only on Docsity!

CS 112 Introduction to

Programming

Lecture #13:

Method Overloading

and Parameter Passing

http://flint.cs.yale.edu/cs112/

Outline

r Admin. and review

q More about defining and using methods

¶ Method header

¶ Overloading and signature

¶ Method parameter passing

¶ Method body

¶ Variable scope and duration

Recap: Methods

r A method should provide a well-defined, easy-to-

understand functionality

m A method takes input (parameters), performs some actions,

and (sometime) returns a value

r Writing a custom method

m Header

m Body

m All methods must be defined inside of a class

Outline

MaximumValue.cs

The program gets three

values from the user

The three values are then passed

to the Maximum method for use

Outline

MaximumValue.cs

Program Output

The Maximum method receives 3

variables and returns the largest one

The use of Math.Max uses the Max

method in class Math. The dot

operator is used to call it.

The Dual Roles of C# Classes

r Program modules:

• a list of (static) method declarations and (static) data

fields

• To make a method static, a programmer applies the

static modifier to the method definition

• The result of each invocation of a class method is

completely determined by the actual parameters (and

static fields of the class)

• To use a static method:

ClassName.MethodName(…);

r Blueprints for generating objects:

• Create an object

• Call methods of the object:

objectName.MethodName(…);

Explicitly Creating Objects

r A class name can be used as a type to

declare an object reference variable

String title;

Random myRandom;

r An object reference variable holds the

address of an object

r No object has been created with the above

declaration

r The object itself must be created using the

new keyword

Creating and Accessing Objects

r We use the new operator to create an object

Random myRandom;

myRandom = new Random();

This calls theThis calls the RandomRandom constructorconstructor , which is, which is

a special method that sets up the objecta special method that sets up the object

r Creating an object is called instantiation

m An object is an instance of a particular class

r To call an ( instance ) method on an object, we

use the variable (not the class), e.g.,

Random generator1 = new Random();

int num = generate1.Next();

Example: the Random class