# Lex program for Decimal to Binary Conversion

Problem: Write a Lex program for Decimal to Binary conversion.

Explanation:
FLEX (Fast Lexical Analyzer Generator) is a tool/computer program for generating lexical analyzers (scanners or lexers) written by Vern Paxson in C around 1987. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language. The function yylex() is the main flex function which runs the Rule Section.

Examples:

```Input: 12
Output: 1100

Input: 115
Output: 1110011

Input: 25
Output: 11001

Input: 220
Output: 11011100 ```

Implementation:

 `/* Lex program for decimal to binary conversion */` ` `  `%{ ` `  ``/* Definition section */` `  ``#include ` `  ``int` `num, r, b=0, p=1; ` `%} ` ` `  `DIGIT [0-9] ` `/* Rule Section */` `%% ` `{DIGIT}+   { num=``atoi``(yytext); ` `             ``while` `(num > 0) ` `             ``{ ` `              ``r= num % 2; ` `              ``b+= r*p; ` `              ``p*= 10; ` `              ``num/= 2; ` `             ``} ` `              ``printf``(``"%d"``, b); ` `            ``} ` `.|\n    ECHO; ` `        `  `%% ` ` `  `// driver code  ` `int` `main() ` `{ ` `    ``yylex(); ` `    ``return` `0; ` `}       `

Output:

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