PLC Project

Language Specification

Program's formatting

The program consists of a sequence of commands. Commands are written with free formatting. Comments, spaces, tabs, and line breaks serve only as delimiters and do not affect the meaning of the program. Comments are bounded by two slashes and the end of the line. Keywords are reserved. Identifiers and keywords are case sensitive.

Variables

Variable's identifiers are composed from letters and digits, and it must start with a letter. Each variable must be declared before it is used. Repeated declaration of a variable with the same name is an error. Variables must have one of the following types: int, float, bool or String. After the variables are declared, they have initial values: 0, 0.0, "" respectively false.

Statements

Following statements are defined:

• ; - empty command.
• type variable, variable, ... ; - declaration of variables, type can be one of: int, float, bool, String
• expression ; - it evaluates given expression, the resulting value of the expression is ignored. Note, there can be some side effects like an assignment to a variable.
• read variable, variable, ... ; - it reads values ​​from standard input and then these values are assigned to corresponding variables. Each of these input values is on a separate line and it is verified, that have an appropriate type.
• write expression, expression, ... ; - it writes values of expressions to standard output. The "\n" character is written after the value of the last expression.
• { statement, statement, ... } - block of statements.
• if (condition) statement [else statement] - conditional statement - condition is an expression with a type: bool. The else part of the statement is optional.
• while (condition) statement - a cycle - condition must be a bool expression. This cycle repeats the given statement while the condition holds (it is true).