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METHOD 2Thanachat Thanomkulabut
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Outline
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Outline
Method Overview Using Method Parameter Passing in Method
No Parameter Pass by value Pass by reference
Parameter Passing Tree4
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Parameter Passing in C#
static <return-type> <method-name>(<<parameter listparameter list>>){ <const/variable declaration>; <statements>;}
Parameter Passing LocationParameter Passing Location
No Parameter6
using System;class NReturned {
static void Hellostatic void HelloMM() {() {
Console.WriteLine(”Hello, Console.WriteLine(”Hello, Mckazine”Mckazine”););
}} static void Main() {
HelloHelloMM();();
HelloHelloMM();();
HelloHelloMM();();
HelloHelloMM();(); }}
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static void Main(){ showtitle(); if(Is_Member() == true) Console.WriteLine(“Welcome my friend”); else Console.WriteLine("Sorry. You cannot admit");}
static void showtitle(){ Console.WriteLine("This is Mc Webboard"); Console.WriteLine("Create by Mckazine");}
static bool Is_Member(){ Console.Write("Are you member (Y/N)"); char member = char.Parse(Console.ReadLine()); if(member == 'Y') return true; else return false;}
Parameter Passing Tree8
Pass by value9
Passing a copy of the variable to the method
Passing value can be both variable and logical expression
Change of variable in the method has no effect on the original
Parameter passing
static void Main(){ ... PrintBox(size); ...}
This is called "pass by value."
static void PrintChar(char c, int n){ ...}
static void PrintBox(int s){ ... PrintChar('x',s-2); ...}
The data value of size is copied to s.
'x' is copied to c.s-2 is evaluated and the resultingvalue is copied to n.
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Parameter passing
static void Main(){ ... PrintBox(size); ...}
static void PrintChar(char c, int n){ ...}
static void PrintBox(int s){ ... PrintChar('x',s-2); ...}
size is an actual parameter.
s is an formal parameter.
'x' and s-2 are actual parameters.
c and n are formal parameters
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Pass by value12
Passing value can be both variable and logical expression
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); ... ...}
Pass by value13
static void Subject (double num, bool okay, int unit){ ... ... ...}static void Main(){ double n=2.5; int limit=0; bool found = true; ... ... ... ... Subject(n, found, limit); ... ...}
Actual Parameter
Formal Parameter
Example 114
static void Main() { Showinfo(“Mc”, 18);}
static void Showinfo(string name,int age){ Console.WriteLine(“Hey {0}!!”,name); Console.WriteLine(“Your age is {0}.”,age);}
name age
“Mc” 18
Hey Mc!!Monitor
Your age is 18.
Example 1 (Extend Edition)15
static void Main() { string username; int born_year; Console.Write("Input your name : "); username = Console.ReadLine(); Console.Write("What year did you born ? "); born_year = int.Parse(Console.ReadLine()); Showinfo(username, 2009-born_year);}
static void Showinfo(string name,int age){ Console.WriteLine(“Hey {0}!!”,name); Console.WriteLine(“Your age is {0}.”,age);}
Pass by value16
Change of variable in the method has no effect on the original
static void Square(int n){ n = n*n; Console.WriteLine("n = {0}",n);}
static void Main(){ int num=5; Square(num); Console.WriteLine("Num = {0}",num); }
5
Num
n
525
n = 25Num = 5
Pass by value17
static void Main() { int x=5,y; y = Add10(x);}
static int Add10(int x){ x = x+10; return x;}
5
x y
x
515
15 15
Self Test I18
Write Method comparefraction Recieve 4 Parameter
Numarator of Fraction1 Denominator of Fraction1 Numarator of Fraction2 Denominator of Fraction2
Return 1 if Fraction1 more than Fraction2 0 if Fraction1 equal to Fraction2 -1 if Fraction1 less than Fraction2
Self Test I19
static int compare_fraction (int n1,int d1,int n2,int d2){
if(n1*d2 > n2*d1) return 1; else if(n1*d2 < n2*d1) return -1; else return 0;}
25
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8 15< n1
d1n2d2
Fraction1
Fraction2
Pass by value : Example20
static void Main(){ int op1, op2; Console.WriteLine(“Enter 2 numbers”); op1 = int.Parse(Console.ReadLine()); op2 = int.Parse(Console.ReadLine()); Compute(op1, op2);}
static void Compute(int op1, int op2){ int i = 1, answer; answer = 1; while (i <= op2) { answer = op1*answer; i = i+1; } Console.WriteLine(answer);}
Parameter Passing Tree21
Pass by reference
Suppose that we want to write a method that swap the values of two variables.
This method does not work. Why?
static void Main(){ ... int x,y; ... swap(x,y);}
static void swap(int a, int b){ int temp; temp = a; a = b; b = temp;}
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Pass by Reference23
Passing the variable's reference to the method
The formal parameter acts as a reference to the actual parameter.
Any changes to the formal parameter effects the actual parameter, since they refer to the same variable.
**use the ref or out keyword** Passing by value, and passing by
reference can be used together in same method
Pass by Reference24
static void subject(ref double num, ref bool okay, double total, int unit){ ... ... ...}
static void Main( ){ double n=6.2, sum=5.4; int limit=10; bool found=true; ... subject(ref n, ref found, sum, limit); ...} n found sum limit
num okay total unit
5A 6B
6.2 TRUE
5.4 10
5A 6B 5.4 10
Passing By Reference (ref)25
static void Add10(ref int x) { x += 10; Console.WriteLine("In the method = {0}",x); }
static void Main() { int myInt = 50; Console.WriteLine("Before calling = {0}",myInt); Add10(ref myInt); Console.WriteLine("After calling = {0}",myInt);}
reference to myInt is passed
to x
So x and myInt are the same variables
myInt
50
Before calling = 50
Output
x
5060
60
In the method = 60After calling = 60
Example126
static void swap(ref int n1, ref int n2) { int temp = n1; n1 = n2; n2 = temp;}
static void Main() { int x = 5,y = 10; Console.WriteLine(“x = {0}, y = {1}”,x,y); swap(ref x,ref y); Console.WriteLine(“x = {0}, y = {1}”,x,y);}
y
10
x
5
x = 5, y = 10
Output
n2
10
n1
5
temp
5 10
10
5
5
x = 10, y = 5
Self Test II27
Write the method exponent( a, b ) Change a to ab
Change b to ba
Example
static void Main() { double x = 2,y = 3; Console.WriteLine(“Before x={0}, y={1}”,x,y);
exponent(ref x,ref y); Console.WriteLine(“After x={0}, y={1}”,x,y);}
Before x=2, y=3
Output
After x=8, y=9
Self Test II28
static void Main() { double x = 2,y = 3; Console.WriteLine(“Before x={0}, y={1}”,x,y);
exponent(ref x,ref y); Console.WriteLine(“After x={0}, y={1}”,x,y);}
static void exponent(ref int a, ref int b) { double temp_a = a; temp_b = b; a = Math.Pow(temp_a,temp_b); b = Math.Pow(temp_b,temp_a);}
Self Test II29
static void Main() { double x = 2,y = 3; Console.WriteLine(“Before x={0}, y={1}”,x,y);
exponent(ref x,ref y); Console.WriteLine(“After x={0}, y={1}”,x,y);}
static void exponent(ref int a, ref int b) { double temp_a = a; temp_b = b; a = Math.Pow(temp_a,temp_b); b = Math.Pow(temp_b,temp_a);}
x
2
y
3
Before x=2, y=3
Output
a
2
b
3
temp_a2
temp_b3 8
8
9
9After x=8, y=9
Self Test III30
Write Method playgame Parameter
Score of player Point of this game
Method Duty Recieve input “W” if player win, “L” if player
lose If player win,
Score of player will be added by point of this game Return true
If player lose Return false
Self Test III31
static bool playgame(ref int score,int point) { string result; Console.Write(“Are you win : ”); result = Console.ReadLine(); if(result == “W”){ score = score + point; return true; } else{ return false; }}
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Pass by value Example
static static void void MainMain(){(){ string string ss;; s s = = "SuperMan2""SuperMan2";; DisplayMovieDisplayMovie((ss);); ConsoleConsole..WriteLineWriteLine((ss); ); }}static static void void DisplayMovieDisplayMovie((string string stst) {) { ConsoleConsole..WriteLineWriteLine(("Movie = {0}""Movie = {0}",,stst);); st st = = "SpiderMan""SpiderMan";;}}
Copy value Copy value ss to to stst
s s = = "SuperMan2""SuperMan2"
Movie = SuperMan2Movie = SuperMan2
st =st ="SuperMan2""SuperMan2"
SuperMan2SuperMan2
st =st =“SpiderMan"“SpiderMan"
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Pass by reference Example
static static void void MainMain(){(){ string string ss;; s s = = "SuperMan2""SuperMan2";; DisplayMovieDisplayMovie((refref ss);); ConsoleConsole..WriteLineWriteLine((ss); ); }}
static static void void DisplayMovieDisplayMovie((refref string string stst) {) { ConsoleConsole..WriteLineWriteLine(("Movie = {0}""Movie = {0}",,stst);); st st = = "SpiderMan""SpiderMan";;}}
ss is referred by is referred by stst
s s = = "SuperMan2""SuperMan2"
Movie = SuperMan2Movie = SuperMan2
st =st ="SuperMan2""SuperMan2"
SpiderManSpiderMan
st =st =“SpiderMan"“SpiderMan"
s =s =“SpiderMan"“SpiderMan"
“ref” disability34
static void add(int a, ref int b, ref int c){ Console.WriteLine(c); c = a + b;}
static void Main(){ int a, b, c; a = 20; b = 10; add(a, ref b, ref c);}
Error
Cannot pass un-initialized
variables
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Passing By Reference refref and outout
refref outout
un-initialized variables are not allowed
any variables are allowed
values are passed to methods via parameter
no values are passed to methods via parameter
refref and outout Keywords
**refref and outout can be used in same method**
“ref” disability But “out” can do it
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static void add(int a, ref int b, ref int c){ c = a + b;}
static void Main(){ int a, b, c; a = 20; b = 10; add(a, ref b, ref c);}
Error
Cannot pass un-initialized
variables
static void Main(){ int a, b, c; a = 20; b = 10; add(a, ref b, out c);}
static void add(int a, ref int b, out int c){ c = a + b;}
a
20
b
10
c
30
a
20
b
10
c
30
Pass by reference (Out)37
static void Main(){ int a, b, c; a = 2; b = 3; c = 4; Ohiyo(a, ref b, out c);
Console.WriteLine(“Finally a = {0}, b = {1}, c = {2}”,a,b,c);}
static void Ohiyo(int x, ref int y, out int z){ x = 2*x; y = 2*y; z = x+y; Console.WriteLine(“Ohiyo x = {0}, y = {1}, z = {2}”, x,y,z);}
a
2
b
3
c
4
x
2
y
3
z
104 6
10
Ohiyo x = 4, y = 6, z = Ohiyo x = 4, y = 6, z = 1010Finally a = 2, b= 6, c = Finally a = 2, b= 6, c = 1010
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Self Test IV38
Write the method ReadInfo Method Duty
Read NAME and SCORE of user , send both back to calling method via parameter of method
Self Test V39
Write the method DivideNumber First parameter is dividend Second parameter is divider Third parameter is remainder of first and
second parameter Return quotient of first and second
parameter
Self Test VI40
Write the method CalDisandSlope First parameter : x-coordinate of point 1 Second parameter : y-coordinate of point 1 Third parameter : x-coorddinate of point 2 Fourth parameter : y-coordinate of point 2 Fifth parameter (out) : distance between
point 1 & 2 Sixth parameter (out) : slope of strenght
line which pass point 1 & 2
ANY QUESTION?
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