1. ASP.NET Programming with C# and SQL Server First Edition Chapter 3 Using Functions, Methods, and Control Structures

2. Objectives In this chapter, you will: Learn how to use functions to organize your C# code Work with the Request object Use if statements, if…else statements, and switch statements to make decisions Use while statements, do…while statements, and for statements to execute code repeatedly ASP.NET Programming with C# and SQL Server, First Edition2

3. Working with Functions Most programming languages allow you to group programming statements into logical units Decision-making and flow-control statements allow you to determine the order in which statements execute in a program Function: a procedure, used to organize a related group of C# statements as a single unit ASP.NET Programming with C# and SQL Server, First Edition3

4. Creating Code Declaration Blocks Code declaration block: contains ASP.NET functions and global variables element: used to create a code declaration block –Must specify the scripting language and where to run the code Syntax: … ASP.NET Programming with C# and SQL Server, First Edition4

5. Defining Functions Must define a function before using it Function definition: the lines that make up a function Syntax: returnDataType functionName(parameters) { statements; } ASP.NET Programming with C# and SQL Server, First Edition5

6. Defining Functions (cont’d.) Return data type: indicates the type of data that the function will provide when it completes –void keyword: specifies that a function or method does not return a value Parameter: a variable used within a function –Placed within the parentheses of a function definition –Must declare the parameter’s data type –Multiple parameters are separated by commas Parameters are used like local variables within the body of the function ASP.NET Programming with C# and SQL Server, First Edition6

7. Calling Functions A function definition does not execute the function Call: to invoke, or execute, the function Function call: the code that calls the function Syntax: functionName(parameters); Arguments: values or variables to be assigned to the function parameters –Also called actual parameters Passing arguments: sending arguments to the parameters ASP.NET Programming with C# and SQL Server, First Edition7

8. Returning Values If a function returns a value, the return value can be assigned to a variable Syntax: variable = functionName(parameters); Return statement: a statement that returns a value to the statement that called the function Syntax: return variable; ASP.NET Programming with C# and SQL Server, First Edition8

9. Understanding Variable Scope Variable scope: where the variable can be used –Determined by where the variable was declared Scope can be global or local Global variable: a variable declared within a code declaration block but outside a function –Available to all parts of the page Local variable: a variable declared inside a function or code render block –Available only within the function or code render block in which it is declared ASP.NET Programming with C# and SQL Server, First Edition9

10. Understanding Variable Scope (cont’d.) Local variables cease to exist when the function or code render block ends If a program contains both a global and a local variable with the same names, the local variable takes precedence when its function is called –Considered poor programming practice to use the same name for both local and global variables ASP.NET Programming with C# and SQL Server, First Edition10

11. Working with the Request Object Request object: a built-in core object that represents the current URL request from a client –Request object uses collections Collection: a data structure similar to an array that stores object properties –To access an object collection: object.collection(“property”) Form collection: contains variables representing form elements from a Web page that was submitted with a method of “post” –Example: Request.Form[“name”] ASP.NET Programming with C# and SQL Server, First Edition11

12. Working with the Request Object (cont’d.) ASP.NET Programming with C# and SQL Server, First Edition12 Table 3-1: Common collections of the Request object

13. QueryString collection: contains variables representing form elements from a Web page that was submitted with a method of “get” Example: Request.QueryString[“name”] A query string on a URL will also assign the name=value pairs to the Request.QueryString collection Count property: returns the number of variables in a collection Example: Request.Form.Count ASP.NET Programming with C# and SQL Server, First Edition13 Working with the Request Object (cont’d.)

14. Making Decisions Decision making (or flow control): the process of determining the order in which statements execute in a program or determining which sets of statements execute if statement: most common type of decision- making statement ASP.NET Programming with C# and SQL Server, First Edition14

15. if Statements if statement: used to execute specific programming code based on the result of a conditional expression –If the conditional expression is true, the statements will be executed Syntax: if (conditional expression) statement; Command block: a set of statements contained within a set of braces –Can be used anywhere a single statement is used ASP.NET Programming with C# and SQL Server, First Edition15

16. if…else Statements if…else statement: executes one set of statements if the conditional expression is true or a different set of statements if the conditional expression is false –Only one set of statements will be executed Syntax: if (conditional expression) statement; else statement; ASP.NET Programming with C# and SQL Server, First Edition16

17. if…else Statements (cont’d.) With command blocks: if (conditional expression) { statements; } else { statements; } ASP.NET Programming with C# and SQL Server, First Edition17

18. Nested if and if…else statements Nested decision-making structure: when one decision-making structure is contained within another decision-making structure –Allows the evaluation of more than one conditional expression Example: if (condition-1) if (condition-2) statement; ASP.NET Programming with C# and SQL Server, First Edition18

19. switch Statement switch statement: executes a specific set of statements depending on the value of an expression –Compares the value of an expression with the value in a case label case label: represents a specific value and contains code that executes if the switch’s expression matches in value Can be used instead of a set of if or if…else statements ASP.NET Programming with C# and SQL Server, First Edition19

20. switch Statement (cont’d.) Syntax: switch (expression) { case label: statement(s); break; case label: statement(s); break; default: statement(s); } ASP.NET Programming with C# and SQL Server, First Edition20

21. switch Statement (cont’d.) default label: contains statements that execute when no match is found in the case labels Must include a break statement to stop processing after the desired statements have been executed –Without a break statement, the rest of the code in the following case labels will also be executed ASP.NET Programming with C# and SQL Server, First Edition21

22. Repeating Code Loop statement: a control structure that repeatedly executes a statement or series of statements while a condition holds Three types of loop statements: –while –do…while –for ASP.NET Programming with C# and SQL Server, First Edition22

23. while Statements while statement: repeats a set of statements as long as a given conditional expression evaluates to true –When condition becomes false, the loop ends Syntax: while (conditional expression) { statement(s); } Iteration: a repetition of the looping statement ASP.NET Programming with C# and SQL Server, First Edition23

24. while Statements (cont’d.) Counter: a variable that increments or decrements with each iteration of a loop statement To ensure that the while statement will eventually end, you must have code that will change the value of the conditional expression Infinite loop: a loop statement that never ends because its conditional expression is never false A while statement may not execute at all if the expression is initially false ASP.NET Programming with C# and SQL Server, First Edition24

25. do…while Statements do…while statement: executes its statements once, and then repeats the execution as long as a conditional expression evaluates to true Syntax: do { statement(s); } while (conditional expression); In the do…while statement, the statements execute before the conditional expression is evaluated –A do…while loop always executes at least once ASP.NET Programming with C# and SQL Server, First Edition25

26. for Statements for statement: used for repeating a set of statements as long as a given conditional expression evaluates to true –Utilizes a counter whose value changes with each iteration Syntax: for (counter declaration and initialization; condition; update statement) { statement(s); } ASP.NET Programming with C# and SQL Server, First Edition26

27. for Statements (cont’d.) Counter variable in a for statement is updated automatically with each iteration of the loop for statement is usually used when you know (or can programmatically determine) exactly how many iterations are required ASP.NET Programming with C# and SQL Server, First Edition27

28. Using continue Statements to Restart Execution continue statement: stops the current iteration of the loop, but allows the loop to continue with a new iteration –Allows you to skip some statements in the loop body in a single iteration without stopping the looping ASP.NET Programming with C# and SQL Server, First Edition28

29. Summary Use elements to create code declaration blocks to contain ASP.NET functions and global variables Functions organize a group of related C# statements as a single unit Global variables are declared with a code declaration block but outside of a function; are available to all parts of the page Local variables are declared inside of a function or code render block; are available only within the function or block in which it was declared ASP.NET Programming with C# and SQL Server, First Edition29

30. Summary (cont’d.)‏ Request object represents the current URL request from the client Collections are data structures that store object properties Flow control is the process of determining the order in which statements execute if statement executes specific code if a conditional expression evaluates to true if…else statement executes the if clause if the conditional expression is true or executes the else clause if the expression is false ASP.NET Programming with C# and SQL Server, First Edition30

31. Summary (cont’d.)‏ Decision-making structures can be nested within each other switch statement controls program flow by executing specific statements depending on the value of an expression Loop statement repeatedly executes a set of statements while a condition is true or until a condition becomes true while statement repeats a set of statements as long as the condition is true ASP.NET Programming with C# and SQL Server, First Edition31

32. Summary (cont’d.)‏ do…while statement repeats a set of statements as long as the condition is true for statement repeats a set of statements as long as the condition is true continue statement is used to terminate a single loop iteration early but continue the loop with the next iteration ASP.NET Programming with C# and SQL Server, First Edition32