C#: Statements and Methods
Based on slides by Joe Hummel
2UCN Technology: Computer Science – 2014
Contents
“With regards to programming statements and methods, C# offers what you would come to expect from a modern OOPL…”
• Statements• Methods
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Part 1
• Statements
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Statements in C#
• Assignments• Sub routines and functions• Conditionals
– if, switch• Iteration
– for, while, do-while• (Uncontrolled) Control Flow
– return, break, continue, goto
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Examples
x = obj.foo();
if (x > 0 && x < 10) count++;else if (x == -1) ...else { ...}
while (x > 0){ ...
x--;} for (int k = 0; k < 10; k++)
{ ...}
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Other Statements
• C# also includes…– iteration over a data structure (Collection) using foreach– namespace imported using using
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foreach
• Specialised foreach loop for sweeping through collections, e.g. array– Reduces the risk for indexing errors– Allows only read only access to elements
int[] data = { 1, 2, 3, 4, 5 };int sum = 0;
foreach (int x in data){ sum += x;}
foreach
type value collection
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using
• using directive provides access to classes in a namespace without pre-fixing
// before
Workshop.Customer c;c = new Workshop.Customer("joe hummel", 94652);
//after
using Workshop;
Customer c;c = new Customer("joe hummel", 94652);
namespace Workshop{ public class Customer { . . . }
public class Product { . . . }}
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Example
• using directives in the top of the file
/* main.cs */
using System;using Workshop;
public class App{ public static void Main() { Customer c; c = new Customer("joe hummel", 94652); Console.WriteLine( c.ToString() ); }}
namespace Workshop{ public class Customer { . . . }
public class Product { . . . }}
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Part 2
• Methods…
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Types of methods
• Classes may define 2 types of methods:– instance– static
• Instance methods can only be applied to instances (objects) of the class. So an object must be created before the method can be used.
• Static methods may be called using the class name
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Example
• The Array class in FCL– fully-qualified name is System.Array
namespace System{ public class Array { public int GetLength(int dimension) { ... }
public static void Sort(Array a) { ... }
. . .
}}
instance method(no static modifier)
static method(static modifier)
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Method call
• Method call (Array class):
/* main.cs */
using System;
public class App{ public static void Main() { int[] data = { 11, 7, 38, 55, 3 }; Array.Sort(data);
for (int i=0; i<data.GetLength(0); i++) Console.WriteLine(i + ": " + data[i]); }}
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Other static methods that may come handy…
using System;
public class Calculator{ public static void Main() { string input, output; int a, b, sum;
Console.Write("Enter first integer: "); input = Console.ReadLine(); a = Convert.ToInt32(input);
Console.Write("Enter second integer: "); input = Console.ReadLine(); b = Convert.ToInt32(input);
sum = a + b; output = String.Format("{0} + {1} = {2}", a, b, sum); Console.WriteLine(output); }}
• Adding two integers and printing the sum:
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Summing Up
• All the usual statements (known from Java), and a few new ones– assignment, if, for, while, foreach, using
• Two types of methods– instance methods, needs an object– static methods, may be called on the class
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