More on Variables and Subroutines

Introduction Discussion so far has dealt with self- contained subs. Subs can call other subs or functions. A module or macro may have many subs or functions. Variables are not always created in a particular sub or function but may be used by these procedures. Where a variable is created will be the scope of that variable.

Scope of Variables and Subroutines A variable created with a Dim statement inside a sub is called a procedure-level variable. A variable created a the top of a module with a Dim statement is a module-level or global variable. –Every sub in the module has access to this variable. Instead if Dim, you can use Private which also has a module-level scope. Another option is to use Public which is a project-level or global scope. This is often used with two or more modules in a project. Variables declared module or project level scope should not be declared in a sub with a Dim statement. Subroutines by default have a Public scope. When you define a Public sub then any other sub in the entire project can call this sub. Subroutines created using Private are only callable by subs within its module.

Passing Control of Subs The main sub is used to call or invoke the other subs or functions. Subs are called or invoked using the Call statement. The arguments used by the sub are listed in parenthesis after the sub procedure’s name. The use of sub and function procedures is an attempt to modularize a project. Allows you to break up code in smaller parts.

Passing Arguments There are two ways sub procedures can access external variables: –1. by using module-level variables –2. by passing arguments Example 1: Const PI As Double = 22/7 Sub Main() Dim R as Integer, A as Double R = Inputbox(“Enter the radius of a circle”,”Input”) A = Area(R) Range(“A1”).Value = “The Area of the Circle is “ & A End Sub Private Function Area(R as Integer) As Double Area = PI * R^2 End Sub Example 2: Sub Main() Dim R as Integer, A as Double R = Inputbox(“Enter the radius of a circle”,”Input”) A = Area(R) Range(“A1”).Value = “The Area of the Circle is “ & A End Sub Private Function Area(R as Integer) As Double Const PI As Double = 22/7 Area = PI * R^2 End Function

Passing Arguments By Reference and By Value Arguments passed by Reference is the default method and passes a reference to the variable being passed. When variables are passed by Reference, the original value of the variable can be changed permanently. When variables are passed by Value only a copy of the original variable’s contents are available to the calling procedure. Arrays are passed to procedures (Sub or Function) by Reference since the elements are generally manipulated. The physical address in memory cannot be changed and passed by Value. Function subroutines always return either a value, Boolean, or string result. A = Area(R) is an example of invoking a Function. The variable A will also receive the result passed from Area.

Concatenating Names And Random Numbers You can concatenate names two ways: –1. You can use the + sign, “Joe ” + “College” –2. You can use the & symbol, “Joe “ & “College” –The second rendition is the preferred style. Random numbers are generated using the function Rnd. You can use Int function to retrieve the integer portion generated. The actual function generates numbers between 0 and 1. The function Randomize is a seed function that assures the numbers generated each time are random. Example: number = 1 + Int (Rnd * 100) will generate numbers between 1 and 100.

Passing Arguments There are two ways sub procedures can access external variables: –1. by using module-level variables –2. by passing arguments Example 1: Const PI As Double = 22/7 Sub Main() Dim R as Integer, A as Double R = Inputbox(“Enter the radius of a circle”,”Input”) A = Area(R) Range(“A1”).Value = “The Area of the Circle is “ & A End Sub Private Function Area(R as Integer) As Double Area = PI * R^2 End Sub Example 2: Sub Main() Dim R as Integer, A as Double R = Inputbox(“Enter the radius of a circle”,”Input”) A = Area(R) Range(“A1”).Value = “The Area of the Circle is “ & A End Sub Private Function Area(R as Integer) As Double Const PI As Double = 22/7 Area = PI * R^2 End Function

Passing Arguments By Reference and By Value Arguments passed by Reference is the default method and passes a reference to the variable being passed. When variables are passed by Reference, the original value of the variable can be changed permanently. When variables are passed by Value only a copy of the original variable’s contents are available to the calling procedure. Arrays are passed to procedures (Sub or Function) by Reference since the elements are generally manipulated. The physical address in memory cannot be changed and passed by Value. Function subroutines always return either a value, Boolean, or string result. A = Area(R) is an example of invoking a Function. The variable A will also receive the result passed from Area.

Concatenating Names And Random Numbers You can concatenate names two ways: –1. You can use the + sign, “Joe ” + “College” –2. You can use the & symbol, “Joe “ & “College” –The second rendition is the preferred style. Random numbers are generated using the function Rnd. You can use Int function to retrieve the integer portion generated. The actual function generates numbers between 0 and 1. The function Randomize is a seed function that assures the numbers generated each time are random. Example: number = 1 + Int (Rnd * 100) will generate numbers between 1 and 100.