Transcript Chapter 4
Chapter 4 Variables and Constants Variables • In math x = 5, x is the variable • In Computer Programming we create the variable first • Stored memory location • Declaration Statement • Dim snglength As Single Variables • Several types of variables – Single-stores numeric values, may be a decimal – Prefix is sng • Initialized to equal zero • Group like variables • Declare, assign, reassign Variable Assignment • Declare – Dim sngRadius As Single = 10 – sngRadius = 12.3 • Using variables – sngCircleArea = 3.14 * sngRadius ^ 2 TextBox • • • • Obtain values from the user VB Prefix – txt Create a prompt – label How are we going to store information that is inputted? • sngRadius = me.txtradius.text • Create and test Textbox • Val function • sngRadius = Val(me.txtradius.text) • Ensure the variable matches the data type – sngRadius = me.txtradius.text, and it’s a user name • If the textbox is not a number Val will return a 0. • TextChanged event procedure Constants • Exactly like a declaration statement.. – Const sngPi As Single = 3.14 • Values that are never changed • Used exactly like a variable • Something that does not have an obvious name should not be a constant or a variable such as sngradius ^ 2, the squared portion is not obvious. Data Types Short srt, integers Integer int, integers Long lng, large integers Single sng, numbers, decimals Double dbl, large numbers, decimals Decimal dec, many significant digits Data Types Date dtm, month/day/year Char chr, single character/symbol String str, set of characters Boolean bln, represents true or false Data Type • Double check the data type: Integers round to the nearest whole number • Dim intX As Integer = 6.7 – intX = 7 Scope • Global and Local Variables • Scope of a Variable – is the set of statements that can use the variable. • Local Declaration – a declaration at the beginning of a procedure where the variable can only be used “locally” • Global Declaration – a declaration placed at the beginning of the program that can be used in any procedure throughout the program. Division Operators • Integer division returns the whole number – intX = 20\7, ‘intX = 2 • Modulus division returns the remainder – intX = 20 mod 7, ‘intX = 6 Programming Errors • Three types of errors – Syntax errors – Logic Errors – Run-Time errors Creating Breakpoints • Stopping points to analyze the computer thought process • Program execution stops at the first breakpoint • Either Add Watch or view the autos window • VB