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Lex program to Count the Positive numbers, Negative numbers and Fractions

  • Last Updated : 01 May, 2019

Problem : Write a Lex program to count the positive numbers, negative numbers and fractions

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.

Prerequisite: Flex (Fast lexical Analyzer Generator)

Examples:

Input: 2 -8 -2.5 8.5 
Output: No. of positive numbers: 1
        No. of Negative numbers: 1
        No. of Positive numbers in fractions: 1
        No. of Negative numbers in fractions: 1 

Input: 1 2 3 -4 -5 6.5 7.5 
Output: No. of positive numbers: 3
        No. of Negative numbers: 2
        No. of Positive numbers in fractions: 2
        No. of Negative numbers in fractions: 0 

Implementation:






/* Lex program to Count the Positive numbers, 
      - Negative numbers and Fractions  */
  
%{
     /* Definition section */
    int postiveno=0;
    int negtiveno=0;
    int positivefractions=0;
    int negativefractions=0;
%}
  
/* Rule Section */
DIGIT [0-9]
%%
  
\+?{DIGIT}+             postiveno++;
-{DIGIT}+               negtiveno++;
  
\+?{DIGIT}*\.{DIGIT}+   positivefractions++;
-{DIGIT}*\.{DIGIT}+     negativefractions++;
. ;   
%%
  
// driver code
int main()
{
    yylex();
    printf("\nNo. of positive numbers: %d", postiveno);
    printf("\nNo. of Negative numbers: %d", negtiveno);
    printf("\nNo. of Positive numbers in fractions: %d", positivefractions);
    printf("\nNo. of Negative numbers in fractions: %d\n", negativefractions);
    return 0;
}

Output:

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