Nell’iperspazio con Rocket: il Framework Web di Rust!
09 Methods
1. MethodsMethods
Subroutines in Computer ProgrammingSubroutines in Computer Programming
Svetlin NakovSvetlin Nakov
Telerik CorporationTelerik Corporation
www.telerik.comwww.telerik.com
2. Table of ContentsTable of Contents
1.1. Using MethodsUsing Methods
What is a Method? Why to Use Methods?What is a Method? Why to Use Methods?
Declaring and Creating MethodsDeclaring and Creating Methods
Calling MethodsCalling Methods
1.1. Methods with ParametersMethods with Parameters
Passing ParametersPassing Parameters
Returning ValuesReturning Values
1.1. Best PracticesBest Practices
2
3. What is a Method?What is a Method?
AA methodmethod is a kind of building block that solvesis a kind of building block that solves
a small problema small problem
A piece of code that has a name and can beA piece of code that has a name and can be
called from the other codecalled from the other code
Can take parameters and return a valueCan take parameters and return a value
Methods allow programmers to construct largeMethods allow programmers to construct large
programs from simple piecesprograms from simple pieces
Methods are also known asMethods are also known as functionsfunctions,,
proceduresprocedures, and, and subroutinessubroutines
3
4. Why to Use Methods?Why to Use Methods?
More manageable programmingMore manageable programming
Split large problems into small piecesSplit large problems into small pieces
Better organization of the programBetter organization of the program
Improve code readabilityImprove code readability
Improve code understandabilityImprove code understandability
Avoiding repeating codeAvoiding repeating code
Improve code maintainabilityImprove code maintainability
Code reusabilityCode reusability
Using existing methods several timesUsing existing methods several times
4
6. Declaring and Creating MethodsDeclaring and Creating Methods
Each method has aEach method has a namename
It is used to call the methodIt is used to call the method
Describes its purposeDescribes its purpose
static void PrintLogo()static void PrintLogo()
{{
Console.WriteLine("Telerik Corp.");Console.WriteLine("Telerik Corp.");
Console.WriteLine("www.telerik.com");Console.WriteLine("www.telerik.com");
}}
MethodMethod
namename
6
7. Declaring and Creating Methods (2)Declaring and Creating Methods (2)
Methods declaredMethods declared staticstatic can be called bycan be called by
any other method (static or not)any other method (static or not)
This will be discussed later in detailsThis will be discussed later in details
The keywordThe keyword voidvoid means that the methodmeans that the method
does not return any resultdoes not return any result
static void PrintLogo()static void PrintLogo()
{{
Console.WriteLine("Telerik Corp.");Console.WriteLine("Telerik Corp.");
Console.WriteLine("www.telerik.com");Console.WriteLine("www.telerik.com");
}}
7
8. static void PrintLogo()static void PrintLogo()
{{
Console.WriteLine("Telerik Corp.");Console.WriteLine("Telerik Corp.");
Console.WriteLine("www.telerik.com");Console.WriteLine("www.telerik.com");
}}
Declaring and Creating Methods (3)Declaring and Creating Methods (3)
Each method has aEach method has a bodybody
It contains the programming codeIt contains the programming code
Surrounded bySurrounded by {{ andand }}
MethodMethod
bodybody
8
9. using System;using System;
class MethodExampleclass MethodExample
{{
static void PrintLogo()static void PrintLogo()
{{
Console.WriteLine("Telerik Corp.");Console.WriteLine("Telerik Corp.");
Console.WriteLine("www.telerik.com");Console.WriteLine("www.telerik.com");
}}
static void Main()static void Main()
{{
// ...// ...
}}
}}
Declaring and Creating Methods (4)Declaring and Creating Methods (4)
Methods are always declared inside aMethods are always declared inside a classclass
Main()Main() is also a method like all othersis also a method like all others
9
11. Calling MethodsCalling Methods
To call a method, simply use:To call a method, simply use:
1.1. The method’s nameThe method’s name
2.2. Parentheses (don’t forget them!)Parentheses (don’t forget them!)
3.3. A semicolon (A semicolon (;;))
This will execute the code in the method’sThis will execute the code in the method’s
body and will result in printing the following:body and will result in printing the following:
PrintLogo();PrintLogo();
Telerik Corp.Telerik Corp.
www.telerik.comwww.telerik.com
11
12. Calling Methods (2)Calling Methods (2)
A method can be called from:A method can be called from:
TheThe Main()Main() methodmethod
Any other methodAny other method
Itself (process known asItself (process known as recursionrecursion))
static void Main()static void Main()
{{
// ...// ...
PrintLogo();PrintLogo();
// ...// ...
}}
12
14. Methods with ParametersMethods with Parameters
Passing Parameters and Returning ValuesPassing Parameters and Returning Values
15. Method ParametersMethod Parameters
To pass information to a method, you can useTo pass information to a method, you can use
parametersparameters (also known as(also known as argumentsarguments))
You can pass zero or several input valuesYou can pass zero or several input values
You can pass values of different typesYou can pass values of different types
Each parameter has name and typeEach parameter has name and type
Parameters are assigned to particular valuesParameters are assigned to particular values
when the method is calledwhen the method is called
Parameters can change the method behaviorParameters can change the method behavior
depending on the passed valuesdepending on the passed values
15
16. Defining and UsingDefining and Using
Method ParametersMethod Parameters
Method’s behavior depends on its parametersMethod’s behavior depends on its parameters
Parameters can be of any typeParameters can be of any type
intint,, doubledouble,, stringstring, etc., etc.
arrays (arrays (intint[][],, double[]double[], etc.), etc.)
static void PrintSign(int number)static void PrintSign(int number)
{{
if (number > 0)if (number > 0)
Console.WriteLine("Positive");Console.WriteLine("Positive");
else if (number < 0)else if (number < 0)
Console.WriteLine("Negative");Console.WriteLine("Negative");
elseelse
Console.WriteLine("Zero");Console.WriteLine("Zero");
}}
16
17. Defining and UsingDefining and Using
Method Parameters (2)Method Parameters (2)
Methods can have as many parameters asMethods can have as many parameters as
needed:needed:
The following syntax is not valid:The following syntax is not valid:
static void PrintMax(float number1, float number2)static void PrintMax(float number1, float number2)
{{
float max = number1;float max = number1;
if (number2 > number1)if (number2 > number1)
max = number2;max = number2;
Console.WriteLine("Maximal number: {0}", max);Console.WriteLine("Maximal number: {0}", max);
}}
static void PrintMax(float number1, number2)static void PrintMax(float number1, number2)
17
18. Calling MethodsCalling Methods
with Parameterswith Parameters
To call a method and pass values to itsTo call a method and pass values to its
parameters:parameters:
Use the method’s name, followed by a list ofUse the method’s name, followed by a list of
expressions for each parameterexpressions for each parameter
Examples:Examples:
PrintSign(-5);PrintSign(-5);
PrintSign(balance);PrintSign(balance);
PrintSign(2+3);PrintSign(2+3);
PrintMax(100, 200);PrintMax(100, 200);
PrintMax(oldQuantity * 1.5, quantity * 2);PrintMax(oldQuantity * 1.5, quantity * 2);
18
19. Calling MethodsCalling Methods
with Parameters (2)with Parameters (2)
Expressions must be of the same type asExpressions must be of the same type as
method’s parameters (or compatible)method’s parameters (or compatible)
If the method requires aIf the method requires a floatfloat expression, youexpression, you
can passcan pass intint insteadinstead
Use the same order like in method declarationUse the same order like in method declaration
For methods with no parameters do not forgetFor methods with no parameters do not forget
the parenthesesthe parentheses
19
23. Months – ExampleMonths – Example
Display the period between two months in aDisplay the period between two months in a
user-friendly wayuser-friendly way
using System;using System;
class MonthsExampleclass MonthsExample
{{
static void SayMonth(int month)static void SayMonth(int month)
{{
string[] monthNames = new string[] {string[] monthNames = new string[] {
"January", "February", "March","January", "February", "March",
"April", "May", "June", "July","April", "May", "June", "July",
"August", "September", "October","August", "September", "October",
"November", "December"};"November", "December"};
Console.Write(monthNames[month-1]);Console.Write(monthNames[month-1]);
}}
(the example continues)(the example continues)
23
24. Months – Example (2)Months – Example (2)
static void SayPeriod(int startMonth, int endMonth)static void SayPeriod(int startMonth, int endMonth)
{{
int period = endMonth - startMonth;int period = endMonth - startMonth;
if (period < 0)if (period < 0)
{{
period = period + 12;period = period + 12;
// From December to January the// From December to January the
// period is 1 month, not -11!// period is 1 month, not -11!
}}
Console.Write("There are {0} " + months from ", period);Console.Write("There are {0} " + months from ", period);
SayMonth(startMonth);SayMonth(startMonth);
Console.Write(" to ");Console.Write(" to ");
SayMonth(endMonth);SayMonth(endMonth);
}}
}}
24
27. Printing Triangle – ExamplePrinting Triangle – Example
static void Main()static void Main()
{{
int n = int.Parse(Console.ReadLine());int n = int.Parse(Console.ReadLine());
for (int line = 1; line <= n; line++)for (int line = 1; line <= n; line++)
PrintLine(1, line);PrintLine(1, line);
for (int line = n-1; line >= 1; line--)for (int line = n-1; line >= 1; line--)
PrintLine(1, line);PrintLine(1, line);
}}
static void PrintLine(int start, int end)static void PrintLine(int start, int end)
{{
for (int i = start; i <= end; i++)for (int i = start; i <= end; i++)
{{
Console.Write(" {0}", i);Console.Write(" {0}", i);
}}
Console.WriteLine();Console.WriteLine();
}}
27
29. Optional ParametersOptional Parameters
C# 4.0 supports optional parameters with defaultC# 4.0 supports optional parameters with default
values:values:
The above method can be called in several ways:The above method can be called in several ways:
static void PrintNumbers(int start=0; int end=100)
{{
for (int i=start; i<=end; i++)for (int i=start; i<=end; i++)
{{
Console.Write("{0} ", i);Console.Write("{0} ", i);
}}
}}
PrintNumbers(5, 10);
PrintNumbers(15);
PrintNumbers();
PrintNumbers(end: 40, start: 35);
29
32. Returning Values From MethodsReturning Values From Methods
A method canA method can returnreturn a value to its callera value to its caller
Returned value:Returned value:
Can be assigned to a variable:Can be assigned to a variable:
Can be used in expressions:Can be used in expressions:
Can be passed to another method:Can be passed to another method:
string message = Console.ReadLine();string message = Console.ReadLine();
// Console.ReadLine() returns a string// Console.ReadLine() returns a string
float price = GetPrice() * quantity * 1.20;float price = GetPrice() * quantity * 1.20;
int age = int.Parse(Console.ReadLine());int age = int.Parse(Console.ReadLine());
32
33. Defining MethodsDefining Methods
That Return a ValueThat Return a Value
Instead ofInstead of voidvoid, specify the type of data to return, specify the type of data to return
Methods can return any type of data (Methods can return any type of data (intint,,
stringstring, array, etc.), array, etc.)
voidvoid methods do not return anythingmethods do not return anything
The combination of method's name, parametersThe combination of method's name, parameters
and return value is calledand return value is called method signaturemethod signature
UseUse returnreturn keyword to return a resultkeyword to return a result
static int Multiply(int firstNum, int secondNum)static int Multiply(int firstNum, int secondNum)
{{
return firstNum * secondNum;return firstNum * secondNum;
}}
33
34. TheThe returnreturn StatementStatement
TheThe returnreturn statement:statement:
Immediately terminates method’s executionImmediately terminates method’s execution
Returns specified expression to the callerReturns specified expression to the caller
Example:Example:
To terminateTo terminate voidvoid method, use just:method, use just:
Return can be used several times in a methodReturn can be used several times in a method
bodybody
return -1;
return;
34
39. Positive Numbers – ExamplePositive Numbers – Example
Check if all numbers in a sequence are positive:Check if all numbers in a sequence are positive:
static bool ArePositive(int[] sequence)static bool ArePositive(int[] sequence)
{{
foreach (int number in sequence)foreach (int number in sequence)
{{
if (number <= 0)if (number <= 0)
{{
return false;return false;
}}
}}
return true;return true;
}}
39
41. Data Validation – ExampleData Validation – Example
Validating input data:Validating input data:
using System;using System;
class ValidatingDemoclass ValidatingDemo
{{
static void Main()static void Main()
{{
Console.WriteLine("What time is it?");Console.WriteLine("What time is it?");
Console.Write("Hours: ");Console.Write("Hours: ");
int hours = int.Parse(Console.ReadLine());int hours = int.Parse(Console.ReadLine());
Console.Write("Minutes: ");Console.Write("Minutes: ");
int minutes = int.Parse(Console.ReadLine());int minutes = int.Parse(Console.ReadLine());
// (The example continues on the next slide)// (The example continues on the next slide)
41
44. Methods – Best PracticesMethods – Best Practices
Each method should perform a single,Each method should perform a single,
well-defined taskwell-defined task
Method’s name should describe thatMethod’s name should describe that
task in a clear and non-ambiguous waytask in a clear and non-ambiguous way
Good examples:Good examples: CalculatePriceCalculatePrice,, ReadNameReadName
Bad examples:Bad examples: ff,, g1g1,, ProcessProcess
In C# methods should start with capital letterIn C# methods should start with capital letter
Avoid methods longer than one screenAvoid methods longer than one screen
Split them to several shorter methodsSplit them to several shorter methods
44
45. SummarySummary
Break large programs into simple methodsBreak large programs into simple methods
that solve small sub-problemsthat solve small sub-problems
Methods consist of declaration and bodyMethods consist of declaration and body
Methods are invoked by their nameMethods are invoked by their name
Methods can accept parametersMethods can accept parameters
Parameters take actual values when calling aParameters take actual values when calling a
methodmethod
Methods can return a value or nothingMethods can return a value or nothing
45
47. ExercisesExercises
1.1. Write a method that asks the user for his name andWrite a method that asks the user for his name and
prints “Hello, <name>” (for example, “Hello,prints “Hello, <name>” (for example, “Hello,
Peter!”). Write a program to test this method.Peter!”). Write a program to test this method.
2.2. Write a methodWrite a method GetMax()GetMax() with two parameters thatwith two parameters that
returns the bigger of two integers. Write a programreturns the bigger of two integers. Write a program
that reads 3 integers from the console and prints thethat reads 3 integers from the console and prints the
biggest of them using the methodbiggest of them using the method GetMax()GetMax()..
3.3. Write a method that returns the last digit of givenWrite a method that returns the last digit of given
integer as an English word. Examples: 512integer as an English word. Examples: 512 "two","two",
10241024 "four", 12309"four", 12309 "nine"."nine".
47
48. Exercises (2)Exercises (2)
4.4. Write a method that counts how many times givenWrite a method that counts how many times given
number appears in given array. Write a test programnumber appears in given array. Write a test program
to check if the method is working correctly.to check if the method is working correctly.
5.5. Write a method that checks if the element at givenWrite a method that checks if the element at given
position in given array of integers is bigger than itsposition in given array of integers is bigger than its
two neighbors (when such exist).two neighbors (when such exist).
6.6. Write a method that returns the index of the firstWrite a method that returns the index of the first
element in array that is bigger than its neighbors, orelement in array that is bigger than its neighbors, or
-1, if there’s no such element.-1, if there’s no such element.
Use the method from the previous exercise.Use the method from the previous exercise.
48
49. Exercises (3)Exercises (3)
7.7. Write a method that reverses the digits of givenWrite a method that reverses the digits of given
decimal number. Example: 256decimal number. Example: 256 652652
8.8. Write a method that adds two positive integerWrite a method that adds two positive integer
numbers represented as arrays of digits (each arraynumbers represented as arrays of digits (each array
elementelement arr[iarr[i]] contains a digit; the last digit iscontains a digit; the last digit is
kept inkept in arr[0]arr[0]). Each of the numbers that will be). Each of the numbers that will be
added could have up to 10 000 digits.added could have up to 10 000 digits.
9.9. Write a method that return the maximal element inWrite a method that return the maximal element in
a portion of array of integers starting at given index.a portion of array of integers starting at given index.
Using it write another method that sorts an array inUsing it write another method that sorts an array in
ascending / descending order.ascending / descending order.
49
50. Exercises (4)Exercises (4)
10.10. Write a program to calculateWrite a program to calculate n!n! for eachfor each nn in thein the
rangerange [1..100][1..100]. Hint: Implement first a method. Hint: Implement first a method
that multiplies a number represented as array ofthat multiplies a number represented as array of
digits by given integer number.digits by given integer number.
11.11. Write a method that adds two polynomials.Write a method that adds two polynomials.
Represent them as arrays of their coefficients as inRepresent them as arrays of their coefficients as in
the example below:the example below:
xx22
+ 5 = 1+ 5 = 1xx22
+ 0+ 0xx + 5+ 5
10.10. Extend the program to support also subtraction andExtend the program to support also subtraction and
multiplication of polynomials.multiplication of polynomials.
55 00 11
50
51. Exercises (5)Exercises (5)
13.13. Write a program that can solve these tasks:Write a program that can solve these tasks:
Reverses the digits of a numberReverses the digits of a number
Calculates the average of a sequence of integersCalculates the average of a sequence of integers
Solves a linear equationSolves a linear equation aa ** xx ++ bb = 0= 0
Create appropriate methods.Create appropriate methods.
Provide a simple text-based menu for the user toProvide a simple text-based menu for the user to
choose which task to solve.choose which task to solve.
Validate the input data:Validate the input data:
The decimal number should be non-negativeThe decimal number should be non-negative
The sequence should not be emptyThe sequence should not be empty
aa should not be equal toshould not be equal to 00
51
