Write a lex program that detects and counts the pattern that starts with an uppercase letter, ends with a lowercase letter - lex

Question

I understood the problem and written the below code. My code works and it prints the number of detected valid and invalid patterns when I quit the program with ctrl+z.
Here is my code:
%{
int valid = 0;
int invalid = 0;
%}
%%
([A-Z][a-zA-Z0-9]*[a-z])* {valid++;}
[a-zA-Z0-9]* {invalid++;}
%%
int yywrap(){}
int main(int argc, char **argv[])
{
printf("\n Enter inputs: \n\n");
yylex();
printf("\n\n\tNumber of VALID patterns = %d\n", valid);
printf("\tNumber of invalid patterns = %d\n\n", invalid);
return 0;
}
But I want something like this:
It should print the detected patterns, number of valid patterns and the number of invalid patterns whenever I input a new line.
There should be an EXIT command.

Answer 1

To achieve your goal, you should modify your code like this:
/*** Definition Section ***/
%{
int valid = 0;
int invalid = 0;
%}
/*** Rules Section ***/
%%
([A-Z][a-zA-Z0-9]*[a-z])* {printf("\n\tPattern Detected: %s ", yytext); valid++;}
[a-zA-Z0-9]* {invalid++;}
"\n" {
printf("\n\n\tNumber of VALID patterns = %d\n", valid);
printf("\tNumber of invalid patterns = %d\n\n", invalid);
valid = 0;
invalid = 0;
}
EXIT__ return 0;
%%
/*** User code section***/
int yywrap(){}
int main(int argc, char **argv[])
{
printf("\n Enter inputs: \n\n");
yylex();
return 0;
}
Here main change comes in the rule section.
Rule-1: ([A-Z][a-zA-Z0-9]*[a-z])* It detect and count valid patterns that starts with an uppercase letter, ends with a lowercase letter. In action, it prints the detected patterns and does the counting job too. Here yytext contains the text in the buffer, for this rule, it's the detected pattern.
Rule-2: [a-zA-Z0-9]* Keep a track of invalid patterns. It will help to prevent returning unmatched patterns.
Rule-3: "\n" It detects when you input a new line. In action, it prints the detected patterns, the number of valid patterns, and the number of invalid patterns whenever I input a new line. Also, reset the variables for counting to zero for the next line of input.
Rule-4: EXIT__ whenever you will input this exact command, the program will exit.
You can avoid printing the numbers of valid and invalid patterns inside the main function in the user code section.
But if you want to print the numbers of detected valid and invalid patterns at the end too, then this program will require a few modifications.