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Resources » Articles/Knowledge Sharing » Education »
Compiler Design Lab Program -2
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PROGRAM FOR LEXICAL ANALYSIS
#include
#include
#include
#include
#include
#define SIZE 128
#define NONE -1
#define EOS '\0'
#define NUM 256
#define KEYWORD 257
#define PAREN 258
#define ID 259
#define ASSIGN 260
#define REL_OP 261
#define DONE 262
#define MAX 999
char lexemes[MAX];
char buffer[SIZE];
int lastchar=-1;
int lastentry=0;
int tokenval=NONE;
int lineno=1;
struct entry
{
char *lexptr;
int token;
}
symtable[100];
struct entry keywords[]={"if",KEYWORD,"else",KEYWORD,"for",KEYWORD,"int",KEYWORD,
"float",KEYWORD,"double",KEYWORD,"char",KEYWORD,
"struct",KEYWORD,"return",KEYWORD,0,0};
void Error_Message(char *m)
{
fprintf(stderr,"line %d: %s\n",lineno,m);
exit(1);
}
int look_up(char s[])
{
int k;
for(k=lastentry;k>0;k=k-1)
if(strcmp(symtable[k].lexptr,s)==0)
return k;
return 0;
}
int insert(char s[],int tok)
{
int len;
len = strlen(s);
if(lastentry+1>=MAX)
Error_Message("Symbol Table Is Full");
if(lastchar +len+1>=MAX)
Error_Message("Lexemes Array Is Full");
lastentry=lastentry+1;
symtable[lastentry].token=tok;
symtable[lastentry].lexptr=&lexemes[lastchar+1];
lastchar=lastchar + len + 1;
strcpy(symtable[lastentry].lexptr,s);
return lastentry;
}
void initialize()
{
struct entry *ptr;
for(ptr=keywords;ptr->token;ptr++)
insert(ptr->lexptr,ptr->token);
}
int lexer()
{
int t;
int val,i=0;
while(1)
{
t=getchar();
if(t==' '||t=='\t');
else if(t=='\n')
lineno=lineno+1;
else if(t=='('||t==')')
return PAREN;
else if(t=='<'||t=='>'||t=='<='||t=='>='||t=='!=')
return REL_OP;
else if(t=='=')
return ASSIGN;
else if(isdigit(t))
{
ungetc(t,stdin);
scanf("%d",&tokenval);
return NUM;
}
else if(isalpha(t))
{
while(isalnum(t))
{
buffer[i]=t;
t=getchar();
i=i+1;
if(i>=SIZE)
Error_Message("Compiler Error");
}
buffer[i]=EOS;
if(t!=EOF)
ungetc(t,stdin);
val=look_up(buffer);
if(val==0)
val=insert(buffer,ID);
tokenval=val;
return symtable[val].token;
}
else if(t==EOF)
return DONE;
else
{
tokenval=NONE;
return t;
}}}
void main()
{
int lookahead;
char ans;
clrscr();
printf("\n\t\t program for lexical Analysis\n");
initialize();
printf("\n Enter the expression and put the ; at the end");
printf("\n Press control z to terminate");
lookahead=lexer();
while(lookahead!=DONE)
{
if(lookahead==NUM)
{
printf("\n Number:");
printf("%d",tokenval);
}
if(lookahead=='+'||lookahead=='-'||lookahead=='*'||lookahead=='/')
printf("\n Operator");
if(lookahead==PAREN)
printf("\n Parenthesis");
if(lookahead==ID)
{
printf("\n Identifiers");
printf("%s",symtable[tokenval].lexptr);
}
if(lookahead==KEYWORD)
printf("\n Keyword");
if(lookahead==ASSIGN)
printf("\n Assignment operator");
if(lookahead==REL_OP)
printf("\n Relational Operator");
lookahead=lexer();
}
}
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