PLC Project

Language Specification

Program's formatting

The program consists of a sequence of commands. Commands are written with free formating. Comments, spaces, tabs and line breaks serve only as delimiters and do not affect the meaning of the program. Commnets 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, boolean or String. After the declaration, variables have initial values: 0, 0.0, "" respectivelly False.

Statements

Following statements are defined:

• ; - empty command;
• type variable, variable, ... ; - declaration of variables, type can be one of: int, float, boolean, 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 coresponding variables. Each readed value 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.
• Command block - block starts {and ends}
• if (condition) statements else statements

Conditional statement, condition must be a Boolean expression. Commands indicate a sequence of commands separated by a semicolon. The else part is optional.

• for (expression_1; condition; expression_2) statements

Cycle statement, condition must be a Boolean expression. The first expression is executed before the start of the cycle, the second after each step of the cycle.