Welcome to Computer Programming II! Computer Programming II Summer 2015

Purpose Computer Programming II has been completely redesigned to better align with real world uses of the C# language outside of gaming. The course will use C#. This language is very similar and based on the C language. This PowerPoint will begin to cover differences between Visual Basic and C- based languages.

Essential Standard Understand variable declaration and syntax  This PowerPoint Loop and If Statements Random Numbers Software Design Life Cycle & Types of Errors

Moving to C# from Visual Basic This PowerPoint reviews variables, decision making statements, arrays, and methods (sub procedures). Major differences between C# and VB are also covered. C# is very different from VB in one KEY way. All statements MUST end with a semicolon (;). If you forget this, your code will not work. Exceptions: IF statements and loops The upside to this is two-fold: 1. Multiple coding statements may be on the same line 2. A long code segment can be spilt up without having to use an underscore like in VB.

Spacing C# Examples int intAge; string strName; Two different statements- same line Long line of code: string query whatever FROM tableName WHERE column = 1"; Both are perfectly valid statements in C#.

Semicolon Exceptions Two exceptions to the semicolon rule: if(x==b)  no semicolon here It is a “clause” - only part of the statement { y=7;  semicolon as normal } while(x< i)  no semicolon here either – again it is a “clause” { intGradeTotal=intGrade;  semicolon as normal }

Declaring a Variable In VB we use the Dim keyword to declare a variable: Dim intAge as Integer C# handles this differently: int intAge; In C# use the following format: DataType variableName; All types are spelled out except integer (int), character (char), and boolean (bool)

C# Examples string strName; char charGrade; int intAge; double dblTaxRate;

Data Types Data TypeStorageValue Range Integer (int)4 Bytes-2,147,483,648 to 2,147,483,647 Double8 Bytes1.7E +/- 308 (15 digits) Decimal16 Bytes1.7E +/- 308 (15 digits) Char1 Byte–128 to 127 by default Boolean (bool)1 ByteTrue or False StringVaries0 to approximately 2 billion Unicode characters

Default Value It is a syntax error in C# to declare a variable then use it before giving it a value. In VB a default value of 0 for a number variable or null for a string is assumed. Example: int intAge = 0; intTotal= intAge + 5;  valid because intAge is given the value of 0 before being used below int intAge; intTotal = intAge + 5;  syntax error because no value was given before it was used

Static and Const In Visual Basic if we wanted a variable to hold its value we used the static keyword in place of Dim. Static works differently in C#. Local variables cannot be declared as static in C#. Const works the same as it does in VB. Using Const a variable’s value cannot be changed once assigned. Example: const double TAXRate = 0.675; (C#) Example: Const TAXRate As Double = (VB)

Coding Blocks In VB we use the End keyword to end coding blocks like IF statements or loops. If a = b Then b=c End If In C#, we use braces so this code block would be written: if(a==b) { b=c; }

Equality Check (==) You might have noticed something on the last slide- a == in the if statement. In VB the assignment operator and equality are the same (=). This is NOT true in C#. The equals sign is solely used for assignment. To check for equality you must use ==. Using = in an if statement to check for equality is a logic error. The code will run properly, but not produce the intended result. (It will always be false.)

Increment Counters In VB to add one to a counter we use varName += 1, for two we use +=2 and so on. (i+=1) This shorthand works in C# as well, but C# provides an additional way to add or subtract one from a counter. i++; i--; ++ adds 1 to the value of i while -- subtracts one. Remember the semicolon is required. To count by 2, or another number, we use the same shorthand as in VB (i+=2).

Try/Catch Try/Catch was used for error checking (exception handling) extensively in VB and is also used in C#, but the format is different. Example: try { Code to try } catch { Code to run if try code fails }

try/catch/finally try { Code to try } catch { Code to run if try code fails } finally { Code to run regardless if the try was successful or not. }

Arrays In VB we use ( ) in array statements. In C# [ ] are used instead. Dim intArray = New Integer(4) {1, 2, 3, 4, 5} (VB) int[] intArray = new int[5] {1,2,3,4,5}; (C#) In VB we put in 1 less than the number of elements we want in the array. This is NOT the case in C#. If we want five elements we use a 5 as shown above. Arrays are still index-based starting at 0.

Conclusion of Part I In this PowerPoint we looked at some differences between C# and Visual Basic. In the next part we will take a look at methods in C#. In the next lesson we will continue our look at differences by looking at loops and if statements.