Feb 2, 2012

K & R C Programs Exercise 5-18.

K and R C, Solution to Exercise 5-18:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
C Program to convert the C declaration into a word description and Make dcl recover from input errors.Read more about C Programming Language .

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#include<stdio.h>
#include<string.h>
#include<ctype.h>
enum { NAME, PARENS, BRACKETS};
enum { NO, YES};
void dcl(void);
void dirdcl(void);
void errmsg(char *);


int gettoken(void);
extern int tokentype;
extern char token[];
extern char name[];
extern char  out[];
extern int prevtoken;

main()
{
 int type;
 char temp[MAXTOKEN];
 while (gettoken() !=EOF) {
  strcy(out, token);
  while ((type = gettoken())  != '\n')
   if(type == PARENS || type == BRACKETS)
    strcat(out, token);
   else if(type == '*') {
    sprintf(temp, "(*%s)", out);
    strcpy(out, temp);
   }else if(type == NAME){
    sprintf(temp, "%s%s",token, out);
    strcpy(out, temp);
   }else
    printf("Invalid input at %s\n",token);
  printf("%s\n",out);
 }
 return 0;
}


//dcl:parse a declarator
void dcl(void)
{
 int ns;
 for(ns = 0; gettoken() == '*';)
  ns++;
 dirdcl();
 while(ns --> 0)
  strcat(out, "pointer to");
}


//dirdcl: parse a direct declaration
void dirdcl(void)
{
 int type;
 if(tokentype == '('){
  dcl();
  if(tokentype != ')')
   errmsg("error:missimg)\n");
 }
 else if(tokentype == NAME)
  strcpy(name,token);
 else
  errmsg("error:expected name or (dcl)\n");
 while((type = gettoken()) == PARENS || type == BRACKETS)
  if(type == PARENS)
   strcat(out, "function returning");
  else {
   strcat(out, "array");
   strcat(out, token);
   strcat(out, "of");
  }
}

//errmsg: prints the error message
void errmsg(char *msg)
{
 printf("%s\n",msg);
 prevtoken = YES;
}


//get token:return next token
int gettoken(void)
{
 int c, getch(void);
 void ungetch(int);
 char *p = token;
 if(prevtoken == YES) {
  prevtoken = NO;
  return tokentype;
 }
 while((c = getch()) == ' ' || c == '\t')
  ;
 if(c == '('){
  if ((c = getch()) == ')'){
   strcpy(token,"()");
   return tokentype = PARENS;
  }
  else{
   ungetch(c);
   return tokentype = '(';
  }
 }
 else if(c == '['){
  for(*p++ = c; (*p++ = getch()) != ']';)
   ;
  *p = '\0';
  return tokentype = BRACKETS;
 }
 else if (isalpha(c)) {
  for(*p++ = c; isalnum(c = getch());)
   *p++ = c;
  *p = '\0';
  ungetch(c);
  return tokentype = NAME;
 } else
  return tokentype = c;
}


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