Lab 2: Your first Flex program

  1. How to use STL stack? 
    #include <stdio.h>
#include <stack>
#include <string>

using namespace std;

int main(void) {
    stack<string> s;

    s.push("1");
    s.push("2");
    s.push("3");
    s.push("4");

    while (!s.empty()) {
	printf("%s\n", s.top().c_str());
	s.pop();
    }
}
  2. A Flex example 
    %{

/*
 * lab2.l
 *
 * To compile, do the following:
 *   $ flex -t lab2.l > lab2.cc && g++ -g lab2.cc -o lab2 -lfl
 *
 * To run, do the following:
 *   $ lab2 < Factorial.java
 */

#include <stdio.h>

%}

%x  COMMENT
ws  [ \t]+

%%

"/*" {
    BEGIN COMMENT;
}

<COMMENT>"*/" {
    BEGIN INITIAL;
}

<COMMENT>.|\n {
    // Ignore all comments
}

[A-Za-z0-9_]+ {
    printf("[%s]\n", yytext);
}

{ws} {
    // Ignore white spaces
}

.|\n

%%

int main(void) {
    yylex();
    return (0);
}
  3. Some Infix to Postfix notation examples (not in particular order)