Implementation of Lexical Analysis on Assignment Statements in C++ Programming Language

A compiler is a computer program that translates computer code written in one programming language (the source language) into another language (the target language). The name compiler is primarily used for programs that translate source code from a high-level programming language to a lower level language [7]. The three main processes of compilation are lexical analysis, syntax analysis and semantic analysis. A compiler has two components, front-end and back-end. Front-end portion of a compiler has to do to main tasks lexical analysis and syntax analysis. On the lexical analysis, input source code are scanned and tokenized into various tokens [6]. In the system, front-end portion of the compiler, lexical analysis is used. There are many token elements in C++ programming language. In this system, line break token, white space tokens (space and tab) and operators (+,-,*,/,=,+= and so on) are used as token elements for the assignment statements of C++ source program. This system is taken all the assignment statements of C++ program as input. Of course, the extracted assignment statements may be literals or values assignment statement (e.g. x=3; or pi= 3.142;), variable assignment statement (e.g. x=y; or x=z;) and expression assignment statement (e.g. a=b+c; or x=y*z; or a=b*(c+d); and produced symbol table, step by step recognized table by using finite state automata and lexeme table.

Executable statements

Executable statements define the actions of functions, procedures and rules. They define the logic and actions needed to support the definition of constraints by acting on parameters, local variables and constants. The shortest possible ‘executable’ statement is just a semicolon. It is called a null statement because it does nothing. Such a statement is not useless, however, as you can use a null statement to stake out territory for future use, or perhaps to make the absence of a statement stand out more clearly as in the example following. …IF a = 13 THEN ; -- do nothing ELSE b := 5 ; -- otherwise give b a value END_IF ;... The Alias statement gives a short name (alias) to an identifier that might be long or clumsy to write. The alias exists only in the scope of the alias statement and references to the alias is the same as writing out the identifier out in full. The assignment statement is used to give a value to a local variable or parameter. The type of the expression assigned to the variable must be compatible with the variable or parameter. Some assignments are shown below. The target variable and the expression being assigned to it are assignment compatible if any of the following hold true: • The types are the same. • The expression results in a type which is a subtype of the type declared for the variable being assigned to. • The type of the variable being assigned to is a select type and the expression results in a type which is a member of that select type. The Case statement executes one (or perhaps zero) statement based on the value of an expression. The statement executed is chosen depending on the value of the Selector. The case statement consists of an expression, which is the case selector and a list of alternative actions, each one preceded by a case label. Agreement between the type of the case label and the case selector is required. The first occurring statement having a case label that evaluates to the same value of the case selector is executed.