Lex program for Decimal to Hexadecimal Conversion

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

Explanation:
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.

Prerequisite: Flex (Fast lexical Analyzer Generator)

Examples:

Input: 12 
Output: C

Input: 116
Output: 74

Input: 55
Output: 37

Input: 212
Output: D4

Implementation:

/* Lex program for decimal to hexadecimal conversion */
  
%{ 
    /* Definition section */
    #include<stdio.h> 
    int num, r, digit=0, count, pcount=0, i; 
    char a[20]; 
%} 
  
DIGIT [0-9] 
/* Rule Section */
%% 
  
{DIGIT}+ { num=atoi(yytext); 
  
        while(num!=0) 
        { 
  
            r=num%16; 
            digit='0'+r; 
            if(digit>'9') 
            digit+=7; 
            a[count++]=digit; 
            num=num/16; 
  
        } 
  
        for(i=count-1;i>=pcount;--i) 
                printf("%c", a[i]); 
                pcount=count; 
        } 
  
.|\n    ECHO; 
         
%% 
  
// driver code 
int main() 
{ 
    yylex(); 
    return 0; 
}       

Output:

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