#Homework 1#

Due date: 2016-04-08

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• Use lex or flex to implement a lexical analyzer to parse a C source code.

  Given a correct C source codes, your program must be able to output tokens found in the source code. The tokens you have to process include:

  1. Reserved words: For example, if, else, for. The complete list of reserved words may be found here. You only need to handle standard C reserved words (keywords). You don't need to handle other platform specific extensions. Also you don't need to handle preprocess directives like #include and #define. Please output reserved words in uppercase, e.g., IF, ELSE, and FOR.
  2. Operators: For example, + and -. You may find the list of operators from here and here. Please enclose an identified operator with brackets, e.g., [+], [-], and [*].
  3. Identifiers: A C identifier starts with a non-digit character from a set containing { _, a-z, A-Z}, and then followed by zero or more digits or characters { _, 0-9, a-z, A-Z}. Suppose you have found an identifier xyz, please output it with a prefix "ID". For example, ID:xyz.
  4. Numbers: For simplicity, we do not separate the process for integer and real numbers. You can simply output a number with a prefix "NUM". For example, NUM:123.
  5. Strings: For simplicity, we treat texts quoted with either single-quotes (') or double-quotes (") as a string literal. But you cannot mix them together, i.e., you cannot start a string with a single-quote but terminate it with a double-quote, and vice-versa. It would be better if your program can handle the escape character (), which treats a followed single-quote or double-quote symbol as a regular character. When your program outputs a string, add a prefix "STR" before the string. For example, STR:string-literal.

• Test Input:

1. test1.c:

   #include <stdio.h> int main() { printf("Hello, World\n"); return(0); }

2. test2.c:

   #include <stdio.h> int factorial(int n) { if(n <= 1) return(1); return(n*factorial(n-1)); } int main() { printf("factorial = %d \n", factorial(10)); return(0); }

3. test3.c:

   #include <stdio.h> int main() { int a, b, n; a = 1; b = 1; n = 13; printf("a = %d \n",a); printf("b = %d \n",b); while(n > 0) { int c; c = a + b; printf("c = %d \n",c); a = b; b = c; n = n-1; } return(0); }

• How to Test Your Code:

  Suppose the executable you generated is hw1.exe, you can feed the sample input into your program and check if your output is correct.

  $ cat input-source-code | ./hw1

  Alternatively, you may use input redirection symbol (<) to pass an input file to your program.

  $ ./hw1 < input-source-code