Yacc semantic action is a sequence of -
Yacc semantic action is a sequence of C Statements.
A program must do more than parse input; it must also produce some output based on the input. In a Bison grammar, a grammar rule can have an action made up of C statements. Each time the parser recognizes a match for that rule, the action is executed.
Yacc (Yet Another Compiler-Compiler) is a computer program for the unix operating system. It is a look ahead left-to-right (LALR) parse generator, generating a parser, the part of a compiler that tries to make syntactic sense of the source code, specifically a LALR parser.
Yacc provides a general tool for describing the input to a computer program. The Yacc user specifies the structures of his input, together with code to be invoked as each such structure is recognized. Yacc turns such a specification into a subroutine that handles the input process; frequently, it is convenient and appropriate to have most of the flow of control in the user's application handled by this subroutine.