Practical Programming

COMP153-06S Arithmetic and Types

Arithmetic

• Note: Lecture notes (and labs) are in the COMP153 folder (G drive) and on the web: www.cs.waikato.ac.nz/~geoff • Operations – Add – Multiply * – Subtract – Divide – Power / + ^ eg: 3^2 is 3 2

Order of operations

• Unless you use parentheses to say otherwise – Power is first – Then multiplication and division done in order from left to right – Then addition and subtraction in order from left to right

Examples

• 2 + 3 * 4 – Is 14, evaluated as 2 + (3 * 4) – If you want the addition done first, then you must write (2 + 3) * 4 • 30 / 2 * 3 – Is 45, done strictly from left to right – If you want this to mean 30 / 6 then you must write 30 / (2 * 3)

Types

• All values stored in a computer have a ‘Type’ – ie: the VB system has to know what kind of value it is dealing with – so it knows what operations can be performed on the value and how much storage to make available for it.

Examples of Types

• Integer – Holds whole numbers, roughly in the range +/- 2 billion – Eg: Button1.Width = 200 • String – Hold sequences of characters – text – Eg: Button1.Text = “Press Me” – VB makes no attempt to ‘understand’ the content of a string

Another Type

• Single and Double – Hold fractional or very large numbers – Eg: 2.34

– 1.5E6 means 1.5 * 10 6 – 2.03E-5 means 2.03 * 10 -5

Operations on Types

• Integer values can have arithmetic operations applied to them • So can single and double values • Interestingly there is an operation that can be applied to String values The + operator joins two strings “ABC” + “DEF” gives “ABCDEF”

Type Conversion

• VB tries to be helpful and convert values from one type to another, in order to make sense of statements. • TextBox1.Text = TextBox2.Text * 3.4

• Doesn’t make sense – we cannot multiply a String by a number • However VB will convert text to number, multiply and convert back

Care

• Automatic conversion doesn’t always do what we want (Prac 2) • We can explicitly do it ourselves – Val(…) converts String to number – Str(…) converts from number to String • Eg: Val(Text1.Text) • Eg: Str(100 * 34)

THE END

of the lecture