to run a C Program gcc filename.c ./a.out to run a lex program lex filename.l gcc lex.yy.c ./a.out to install YACC (bison) sudo apt-get install bison sudo apt-get install gcc flex bison to run a YACC program yacc -d filename.y lex filename.l gcc lex.yy.c y.tab.c -w ./a.out