SP Practical 2

Practical : 2

Subject : System Programming

Aim : Write a Lexical Analyzer (using lex utility for UNIX).

Source Code :

letter [a-zA-Z] 
digit[0-9] 
%% 
{digit}+("E"("+"|"-")?{digit}+)? printf("\n%s\tis real number",yytext); 
{digit}+"."{digit}+("E"("+"|"-")?{digit}+)? printf("\n%s\t is floating pt no ",yytext); 
"if"|"else"|"int"|"char"|"scanf"|"printf"|"switch"|"return"|"struct"|"do"|"while"|"void"|"for"|"float" printf("\n%s\t is keywords",yytext); 
"\a"|"\\n"|"\\b"|"\t"|"\\t"|"\b"|"\\a" printf("\n%s\tis Escape sequences",yytext); 
{letter}({letter}|{digit})* printf("\n%s\tis identifier",yytext); 
"&&"|"<"|">"|"<="|">="|"="|"+"|"-"|"?"|"*"|"/"|"%"|"&"|"||" printf("\n%s\toperator ",yytext); 
"{"|"}"|"["|"]"|"("|")"|"#"|"'"|"."|"\""|"\\"|";"|"," printf("\n%s\t is a special character",yytext); 
"%d"|"%s"|"%c"|"%f"|"%e" printf("\n%s\tis a format specifier",yytext); 
%% 
int yywrap() 
{ 
return 1; 
} 
int main(int argc,char *argv[]) 
{ 
yyin=fopen(argv[1],"r"); 
yylex(); 
fclose(yyin); 
return 0; 
}

Output :