K & R C Programs Exercise 5-20.

K and R C, Solution to Exercise 5-20:
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 expand dcl to handle declarations with function argument types, qualifiers like const, and so on. 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 *);
void dclspec(void);
int typespec(void);
int typeequal(void);
int compare(char **, char**);
void parmdcl(void);

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


//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;
void parmdcl(void);
if(tokentype == '('){
dcl();
if(tokentype != ')')
errmsg("error:missimg)n");
}
else if(tokentype == NAME){
if(name[0] == '')
strcpy(name,token);
}else
prevtoken = YES;
while((type = gettoken()) == PARENS || type == BRACKETS || type == '(')
if(type == PARENS)
strcat(out, "function returning");
else if(type == '('){
strcat(out, "function expecting");
parmdcl();
strcat(out, "and returning");
} else{


strcat(out, "array");
strcat(out, token);
strcat(out, "of");
}
}

//errmsg: prints the error message
void errmsg(char *msg)
{
printf("%sn",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 = '';
return tokentype = BRACKETS;
}
else if (isalpha(c)) {
for(*p++ = c; isalnum(c = getch());)
*p++ = c;
*p = '';
ungetch(c);
return tokentype = NAME;
} else
return tokentype = c;
}



//parmdcl: parse a parameter declarator
void parmdcl(void)
{
do{
dclspec();
}while (tokentype == ',');
if(tokentype != ')')
errmsg("missing ) in parameter declarationn");
}

//dclspec: declaration specification
void dclspec(void)
{
char temp[MAXTOKEN];
temp[0] = '';
gettoken();
do{
if(tokentype != NAME){
prevtoken = YES;
dcl();
}else if(typedesc() == YES){
strcat(temp," ");
strcat(temp, token);
gettoken();
}else if(typeequal() == YES){
strcat(temp," ");
strcat(temp, token);
gettoken();
}else
errmsg("unknown type parameter listn");
}while(tokentype != ',' && tokentype != ')');
strcat(out,temp);
if(tokentype == ',');
strcat(out,",");
}

//typedesc: return yes if token is type-specifier
int typespec(void)
{
static char *types[] = {
"char",
"int",
"void"
};
char *pt = token;
if(bsearch(&pt, types,sizeof(types)/sizeof(char *),
sizeof(char *),compare) == NULL)
return NO;
else
return YES;
}

//typeequal:return YES if token is a type qualifier
int typeequal(void)
{
static char *typeq[] = {
"const",
"volatite"
};
char *pt = token;
if(bsearch(&pt, typeq,sizeof(typeq)/sizeof(char *),
sizeof(char *),compare) == NULL)
return NO;
else
return YES;

}

//compare: compare two strings for bsearch
int compare(char **s, char **s)
{
return strcmp(*s, *t);
}
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