TMBASIC Documentation

if Statement

Syntax

(Single-line form)
"if" ─► Expression ─► "then" ─► CommandStatement ─► EOL
(Multi-line form)
"if" ─► Expression ─► "then" ─► EOL ──┐
    ┌─────────────────────────────────┘
    ▼
Statements
    │◄─────────────────────────────────────────────────────────────┐
    ├───► "else if" ─► Expression ─► "then" ─► EOL ─► Statements ──┘
    │
    ├───► "else" ─► EOL ─► Statements ──┐
    │◄──────────────────────────────────┘
    ▼
"end if" ─► EOL

Usage

An if statement is used to make decisions. It is used in conjunction with Boolean values which represent the result of a decision as true or false. The "if ... then ..." structure works just how it sounds. If a given condition is true, then the given statements are executed. Otherwise the statements are skipped.
Consider the following example.
sub Main()
dim x as Number
input x
if x < 0 then
print "Negative number"
else if x > 0 then
print "Positive number"
else
print "Zero"
end if
end sub
After the user types a number and presses Enter, only one of the three print statements will execute. It may help to view the path of execution using a flow chart.
           ↓                                            
          ▄▀▄                                           
        ▄▀   ▀▄  true      ▄▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█▀
       █  x<0  █───────► ▄▀ print "Negative number" ▄▀  
        ▀▄   ▄▀        ▄█▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▀    
          ▀▄▀                                           
           ↓ false                                      
          ▄▀▄                                           
        ▄▀   ▀▄  true      ▄▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█▀
       █  x>0  █───────► ▄▀ print "Positive number" ▄▀  
        ▀▄   ▄▀        ▄█▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▀    
          ▀▄▀                                           
           ↓ false                                      
    ▄▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█▀                                 
  ▄▀ print "Zero"  ▄▀                                   
▄█▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▀

Single-line form

There is a short form that fits on a single line.
if x = 0 then print "Zero"
This convenience form supports only a single statement.

Multi-line form

The full form is composed of three sections: the if block, the optional else if blocks, and the optional else block.
if <condition> then
<statements>
else if <condition> then
<statements>
else if <condition> then
<statements>
else
<statements>
end if