Lex code to divide C program into Functions and signatures

Question

I was trying to create a Lex program that does the following:

INPUT

float hey1(int a, int b);

OUTPUT

Function: hey1

it returns: float

Signature:

a - float

b - float

With the current knowledge I have of LEX, I decided to input the test file and output the 1st part to another file, which would become the input for the next part. Kindly guide me forward, as I have come to a dead end, and can't proceed forward.

My attempt :-

%{
   FILE *out;
%}

letter    [A-Za-z0-9]

%%
("float"|"void"|"int")" "{letter}*"("       fprintf(out,"Function: %s", yytext) ;
%%

int main()
{
    yyin = fopen("test.c","r") ;
    out=fopen("out.c","w");
    yylex() ;
    fclose(yyin) ;
}

Thanks