final review

Final ReviewAuthor: Thanachat ThanomkulabutEdited by Supaporn Erjongmanee

Final Review22 September 2011

Outline2

Major topics Methods Arrays structs

Major Topics Methods

Input Output Global vs. Local Scope of variables

Array Declare, Create, Initialize, Access Run ‘for’ loop with array Array with methods 1D vs. 2D vs. multiD

Major Topics (cont.)

struct Define, Create, Access Array of struct struct with methods

File I/O Collection

Pre-midterm Topics Data types & Variable declaration Math expression Logical expression

How to write condition If switch-case Loop

while, do…while, for break, continue

Outline6

Major topics Methods Arrays structs

Methods7

Input Output Global vs. Local Scope of variables

8

NamespaceClass

Main()

Method1()

Method2()

Method3()

MethodN()

C# Structure – Multiple Methods

9

Characteristics of Method

Method

Type of Method (Output)

No Returned

valueReturned

value

Parameter Passing (Input)

No Parameter

Pass by value

Pass by reference

ref out

Define Method

static <return-type> <method-name>(<parameter list>){ <const/variable declaration>; <statements>;}

10

Syntax

When see a method, answer the followings:

1. What is method name?2. Are there any input? If so, for each input:

a) what’s data type?b) What’s variable name?c) Is it regular or ‘ref’ or ‘out’?

3. Are there any output? If so, for each output:a) what’s data type?b) What’s variable name to store output?

12

Method Input Input

Name of copied variable can be different from original variable

Data type of copied and original variables must be the same!

static void Subject (double num, bool okay, int unit){ ... ... ...}static void Main() { double n; int limit; bool found; ... ... Subject(12.7, true, (limit*3)+5); ... ...}

Method Input (cont.) Input (cont.)

We must choose input to be Pass by Value or Pass by Reference

Pass by Value Data type + Variable name

Pass by Reference => Value returns automatically. Do not use “return”.

ref + Data type + Variable name Must initialize value of Variable before calling the

methodstatic void sub(int a, ref int b){ b = a - b;}

Define Method

static <return-type> <method-name>(<parameter list>){ <const/variable declaration>; <statements>;}

• return-type can be• void = return no value• int, double, string, … = return value with specified data

type and need return statement inside method 14

14

Syntax

Method Output Output

We must choose input to be Returned Value or Pass by Reference Returned Value: appear before Method name

static returned_data_type Method_name (input_parameter_list) { … } Need “return” as one statement in a method

Pass by Reference: appear in (..) after Method name Value returns automatically. Do not use “return”. ref + Data type + Variable name

Must initialize value of Variable before calling the method out + Data type + Variable name

No need to initialize value of Variable before calling the method Value of variable before calling the method will not be passed into the

method

static void add(int a, ref int b, out int c) { c = a + b;}

static int add(int a, int b) { return a + b;}

Pass by Value

16

Change in copied variable in the method has no effect on the original variable

static void Square(int num){ num = num*num; Console.WriteLine("num = {0}",num);}

static void Main(){ int num=5; Square(num); Console.WriteLine(“num = {0}",num); }

5num

num525

num = 25num = 5

Monitor

Pass by reference17

static void Main(){ int a, b, c; a = 2; b = 3; c = 4; Hello(a, ref b, out c);

Console.WriteLine(“Finally a = {0}, b = {1}, c = {2}”,a,b,c);}

static void Hello (int x, ref int y, out int z){ x = 2*x; y = 2*y; z = x+y; Console.WriteLine(“Hello x = {0}, y = {1}, z = {2}”, x,y,z);}

a2

b3

c4

x

2

y

3

z104 6

10

Hello x = 4, y = 6, z = 10Finally a = 2, b= 6, c = 10

6

Monitor

“Out” does not pass in any

value to method

Examples

18

static void Main() { PrintLine(‘n’, 14);

double width = 5, height = 10; double area = Area(width, height); Console.WriteLine(area); Console.WriteLine(compAve(10,20,30));}

static void PrintLine(char a, int b ) { Console.WriteLine(“{0} is {1}th alphabet”, a, b);}

static double Area(double w, double h) { return w*h;}

static double compAve(int x1, int x2, int x3) { return (x1+x2+x3)/3;}

n is 14th alphabet5020

Monitor

Examples 2

19

static void Main() { char x = ‘p’, y = ‘q’; int p = 3, q = 5; double a=5, b=10, c=0, d, e; sub( p, q, out d); mult( a , b, ref c); switch( ref x, ref y);}

static void sub(int a, int b, out double c) { c = a – b ;}

static void mult(double p, double q, ref double r) { r = p * q;}

static void switch(ref char x1, ref char x2) { char temp = x1; x1 = x2; x2 = temp;}

Methods: Passing outputstatic void Main() { int x = 1, y = 2; Add100_v1(x,y); Console.WriteLine(“{0},{1}”,x,y); Add100_v2(ref x,ref y); Console.WriteLine(“{0},{1}”,x,y); Add100_v3(ref x,y); Console.WriteLine(“{0},{1}”,x,y)}static void Add100_v1(int num, int num2) { num += 100; num2 += 100;}static void Add100_v2(ref int num, ref int num2) { num += 100; num2 += 100;}static void Add100_v3(ref int num, int num2) { num += 100; num2 += 100;}

1,2101,102201,102

Monitor

Methods with ref ref can do:1) pass values into

method2) return the changed

values back

Variables passing with ref need to be initialized before passing.

ref can be used with regular or out

static void Main() { int x = 1, y = 2; int result1; Add_v1(x,y,out result1); Console.WriteLine(result1); int result2; Add_v2(x,y,ref result2); Console.WriteLine(result2);}static void Add_v1(int num, int num2, out num3) { num3 = num + num2;}static void Add_v2(int num, int num2, ref num4) { num4 = num + num2;}

Methods with out • Out can do:• pass the changed values

back.

Variables passing with out DO NOT need to be initialized before passing.

No Initialized value for result1 (using out)

OK!

No initialized value for result2 (using ref)

ERROR!!!!

static void Main() { int x = 1, y = 2; int result1; Add_v1(x,y,out result1); Console.WriteLine(result1); int result2 = 0; Add_v2(result1,y,ref result2); Console.WriteLine(result2);}static void Add_v1(int num, int num2, out num3) { num3 = num + num2;}static void Add_v2(int num, int num2, ref num4) { num4 = num + num2;}

35

Monitor

Methods with out • Out can do:• pass the changed values

back.

Variables passing with out DO NOT need to be initialized before passing.

No Initialized value for result1 (using out)

OK!

Initialized value for result2 (using ref)

OK!

Global vs. Local Variables23

Global variables, constants, structs

namespace

class

Main()

MethodX()

Local variables, constants, statements

Local variables, constants, statements

Global vs. Local Variables (cont.)

24class

Main() Method1()

x y

n

int x;

static int n;

x = 5;y = 12;n = 9;

int y;x = 5;y = 12;n = 9;

Variable Scope: Example #1using System;class ScopeTest { static void Main() { for(int i=0;i<5;i++){ Console.Write(“*”); } Console.Write(i); }}

Scope of this

i starts hereThen ends

here

This line is not in i's

scope

25

Variable Scope: Example #2using System;class ScopeTest { static void Main() { int x; x = 5; }

static void Method1() { Console.WriteLine(x); }}

Scope of this x starts here

Then ends here

This line is not in x's

scope

26

Example 127

class Test { static void Main() { int x = 3; Add10(x); Console.WriteLine(x); } static void Add10(int x){ x += 10;

}}

3Monitor

Method Add10 will not pass new value of ‘x’ back since ‘x’ is not

passed by reference.

Program will show value of variable “x” in

Method Main

Example 128

class Test { static int sum = 0; static void Main() { Console.Write(“sum={0}”,sum); Add(2); Console.Write(“sum={0}”,sum); } static void Add(int y){ sum += y; }}

sum=0Monitor

sum=2

Example 2

Example 129

class Test { static int sum = 0; static void Main() { Console.Write(“sum={0}”,sum); Add(2); Console.Write(“sum={0}”,sum); } static void Add(int y){ sum += y; }}

sum=0Monitor

sum=2

Console.Write(“y={0}”,y);

Error

Example 2

Example 3

30 class Test { static int sum = 0; static void Main() { Console.WriteLine(sum); methodA(); Console.WriteLine(sum); } static void methodA(){ int sum = 5; Console.WriteLine(sum); }}

In Main, value of GLOBAL variable ‘sum’ is used.

In methodA, value of LOCAL variable ‘sum’ is

used.

0Monitor 5

0Does this program work?

Outline31

Major topics Methods Arrays structs

Arrays

Declare, Create, Initialize, Access Run ‘for’ loop with array Array with methods 1D vs. 2D vs. multiD

Array: 1D• Declare array

– int [] arr;• Create array: Must have size

– arr = new int [5];• Declare + create: Must have size

– int [] arr = new int [5];• If we want to initialize, we need to

declare (+create) array first. No need to have size– int [] arr = new int [] {5,6,7,8,9};– int [] arr ={5,6,7,8,9};

Array: 1D34

Which ones are valid C# statements ?1. int [] arrayA = new int[] {3, 6, 9};2. int arrayA = new int[3] {3, 6, 9}; 3. int [] arrayA = new int {3, 6, 9};4. int arrayA = new int {3, 6, 9};5. int [] arrayA = new int[3] ;6. int [] arrayA = new int[] ;7. int [] arrayA = new int[3] {3, 6, 9};

Array: 1D (cont.)• Accessing array: index = integer

– Use index: 0,1,…,size-1• Accessing 1 element in array: arr[index]

– Example: arr[0] = 10;• Accessing many elements in array: ‘for’

– for (int i = 0; i < arr.Length; i++) arr[i] = i+10;

• Only-Read all elements in array– foreach (int x in arr)

Console.WriteLine(x);

Array: 1D (cont.)

• Only-Read all elements in array (cont.)– Assume arr2 is array with double typeint count = 0;foreach (double y in arr2) { if (y > 0) count++;}

String37

String is “array of chars.”string name = “Bossa”;Console.WriteLine(name[0]);Console.WriteLine(name[4-3]);name[4] = ‘m’;

‘B’

‘o’ ‘s’nam

e

0 1 2‘s’3

‘a'

4 BOutput

o

Each element in string is for “reading

only”

Array: 2D• Declare array

– int [,] arr;• Create array: Must have size

– arr = new int [3,2];• Declare + create: Must have size

– int [,] arr = new int [3,2];• If we want to initialize, we need to

declare (+create) array first. No need to have size– int [,] arr = new int [,] {{5,6},{7,8},

{9,0}};– int [,] arr ={{5,6},{7,8},{9,0}};

Array: 2D • Accessing array: 2 indices

– Use row index: 0,1,…,row_size-1– Use column index: 0,1,…,col_size-1

• Accessing 1 element in 2D array: arr[row_index, col_index]– Example: arr[0,1] = 5;

• Get size:– arr.GetLength(0): Number of rows– arr.GetLength(1): Number of columns– arr.Length: Number of total elements

Array: 2D (cont.)

• Accessing all elements in 2D array– Use 2 ‘for’ loops: go through all rows and

all columns– Different index for each ‘for’ loop– for (int i = 0; i < arr.GetLength(0); i++)

for (int j = 0; j < arr.GetLength(1); j++)arr[i,j] = i*10+j;

Array: 2D (cont.)

• Accessing one row (e.g., 3rd row) in 2D array– Use 1 ‘for’ loops to go through all

columns– Fixed row index for given row– ‘i’ index for column– Example: for (int i = 0; i < arr.GetLength(1); i++)

Console.WriteLine(arr[2 , i]);

Array: 2D (cont.)

42

• Accessing one column (e.g., 2nd column) in 2D array– Use 1 ‘for’ loops to go through all rows– Fixed column index for given column– ‘i’ index for row– for (int i = 0; i < arr.GetLength(0); i++)

Console.WriteLine(arr[ i, 1]);

static void Main() { int [] arr = new int [10]; Arr_initial(arr); Display_arr(arr); Add10(arr); Display_arr(arr);}static void Arr_initial (int [] a) { for (int i = 0; i < a.Length; i++) a[i] = i;}static void Add10(int [] a) { for (int i = 0; i < a.Length; i++) a[i] = a[i]+10;}static void Display_arr(int [] a) { for (int i = 0; i < a.Length; i++) Console.Write(“{0},” a[i]); Console.WriteLine();}

0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,

Monitor

Pass array into method without ‘ref’1) Pass the changed values back.2) Can’t pass the new array back

Methods: passing array with no ref

Array is initialized all elements with 0 automatically.

Print out values from first to last elements in array

static void Main() { int [] arr = new int [10]; Arr_initial(arr); Display_arr(arr); Op_arr(arr); Display_arr(arr);}static void Arr_initial (int [] a) { for (int i = 0; i < a.Length; i++) a[i] = i;}static void Op_arr(int [] a) {

a = new int [5];}static void Display_arr(int [] a) { for (int i = 0; i < a.Length; i++) Console.Write(“{0},” a[i]); Console.WriteLine();}

0,1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,

Monitor

Pass array into method without ‘ref’1) Pass the changed values back.2) Can’t pass the new array back

Methods: passing array with no ref

Without ref: new array will not be passed back to Main

Declare new array with 5 elements

static void Main() { int [] arr = new int [10]; Arr_initial(arr); Display_arr(arr); Op_arr(arr); Display_arr(arr);}static void Arr_initial (int [] a) { for (int i = 0; i < a.Length; i++) a[i] = i;}static void Op_arr(int [] a) {

a[0]=100; a = new int [5]; a[1]=1000;}static void Display_arr(int [] a) { for (int i = 0; i < a.Length; i++) Console.Write(“{0},” a[i]); Console.WriteLine();}

0,1,2,3,4,5,6,7,8,9,100,1,2,3,4,5,6,7,8,9,

Monitor

Pass array into method without ‘ref’1) Pass the changed values back.2) Can’t pass the new array back

Methods: passing array with no ref

Without ref: changed values after new array will not be passed back to Main

Declare new array with 5 elements

static void Main() { int [] arr = new int [10]; Arr_initial(arr); Display_arr(arr); Op_arr(ref arr); Display_arr(arr);}

static void Arr_initial (int [] a) { for (int i = 0; i < a.Length; i++) a[i] = i;}static void Op_arr(ref int [] a) {

a = new int [5];}static void Display_arr(int [] a) { for (int i = 0; i < a.Length; i++) Console.Write(“{0},” a[i]); Console.WriteLine();}

0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,

Monitor

Methods: passing array with ref Pass array into method with ‘ref’

1) Pass the changed values back.2) Can pass the new array back

Declare new array with 5 elements

With ref: new array will be passed back to Main

static void Main() { int [] arr = new int [10]; Arr_initial(arr); Display_arr(arr); Op_arr(ref arr); Display_arr(arr);}static void Arr_initial (int [] a) { for (int i = 0; i < a.Length; i++) a[i] = i;}static void Op_arr(ref int [] a) { a[0] = 100;

a = new int [5];a[2]=1000;

}static void Display_arr(int [] a) { for (int i = 0; i < a.Length; i++) Console.Write(“{0},” a[i]); Console.WriteLine();}

0,1,2,3,4,5,6,7,8,9,0,0,1000,0,0,

Monitor

Methods: passing array with ref Pass array into method with ‘ref’

1) Pass the changed values back.2) Can pass the new array back

Declare new array with 5 elements

With ref: changed values after new array will be passed back to Main

Outline48

Major topics Methods Arrays structs

struct

Define, Create, Access Array of struct struct with methods

Define struct

StudentInfo

Name: Paul

Dept: Math

Age: 18

Gender: M

string

string

int

char

struct StudentInfo { public string name; public string dept; public int age; public char gender;}

Must use "struct" keyword

Every struct needs a name

Protection level – for now always use "public”

Members of struct

50

using System;class StructTest {

static void Main() { }}

Create struct: Format I & II

struct_name var_name;

StudentInfo

Name:

Dept:

Age:

Gender:

string

string

int

charStdInfo student

= new StdInfo ();StdInfo student;

struct StdInfo { public string name; public string dept; public int age; public char gender;}

51

struct_name var_name = new struct_name ();

Syntax

student.name = “Paul”;

Console.WriteLine(student.name);52

Access struct

var_name.member_name

PaulMonitor

Name:

Dept:

Age:

Gender:

string

string

int

char

• Assign value

• Display value

Paul StdInfo student;

52

Declare & Create Array of struct

Declare Array

Declare Array of struct

double[] score;score = new double[4];

StdInfo[] student;student = new StdInfo[4];

score0 1 2 3

idnamedept

idnamedept

idnamedept

idnamedept

0 1 2 3

student

struct StdInfo { public int id; public string name; public string dept;}

53

Access Array of struct

Access Array

Access Array of structscore[2] = 5;

student[0].name = ”Paul";

idnamedept

idnamedept

idnamedept

idnamedept

0 1 2 3student

score0 1 2 3

5

student[3].id = 713;

713Paul

54 var_name[index].struct_member

Example : Read 1 Student’s Informationclass StructTest { struct StdInfo { public int id; public string name; public string dept; } static void Main() {

}}

StdInfo student; Console.Write("Input ID: ");student.id = int.Parse(Console.ReadLine());Console.Write("Input Name: ");student.name = Console.ReadLine();Console.Write("Input Dept: ");student.dept = Console.ReadLine();

55

1 student

StdInfo

ID:

Name:

Dept:

int

string

string

Example : Read 50 Students’ Informationclass StructTest { struct StdInfo { public int id; public string name; public string dept; } static void Main() {

}}

StdInfo student; Console.Write("Input ID: ");student.id = int.Parse(Console.ReadLine());Console.Write("Input Name: ");student.name = Console.ReadLine();Console.Write("Input Dept: ");student.dept = Console.ReadLine();

56

StdInfo[] student = new StdInfo[50];for(int i=0;i<50;i++){ Console.Write("Input ID: "); student[i].id = int.Parse(Console.ReadLine()); Console.Write("Input ์Name: "); student[i].name = Console.ReadLine(); Console.Write("Input Dept: "); student[i].dept = Console.ReadLine();}

StdInfo

ID:

Name:

Dept:

int

string

string

50 students

Example: Display names of Math students

Display names of students from Math department

for(int i=0;i<50;i++){

if(student[i].dept == ”Math") Console.WriteLine(student[i].name);

}

idnamedept

601 idnamedept

623…

idnamedept

PamMath

0 1 49student

713BobPaul

Math English

57

57

Methods: passing with structstruct complex_num {

public double real; public double imag; }static void Main() { complex_num num1, num2; assign_complex(5,2,out num1); assign_complex(1,7,out num2); display_complex(num1); add_complex(ref num1, num2); display_complex(num1);}static void assign_complex(double r, double im, out complex_num n) { n.real = r; n.imag = im; }static void add_complex(ref complex_num n, complex_num n2) { n.real = n.real + n2.real; n.imag = n.imag + n2.imag; }static void display_complex(complex_num n) { Console.WriteLine(“{0}+{1}i”,n.real, n.imag); }

5+2i6+9i

Monitor

Similar to regular variables, we can use struct to pass by value or pass by reference (ref or out).Replace data type with struct name

Good Luck