Section 6.3 Arrays of Structures

Program

#include <stdio.h>
#include <ctype.h>
#include <string.h>

#define MAXWORD 100

struct key {
    char *word;
    int count;
} keytab[] =  {
    "auto", 0,
    "break", 0,
    "case", 0,
    "char", 0,
    "const", 0,
    "continue", 0,
    "default", 0,
    "unsigned", 0,
    "void", 0,
    "volatile", 0,
    "while", 0,
    "printf", 0, /* Figure out why printf is a special case */
};


#define NKEYS (sizeof keytab / sizeof(struct key))

int mgetword(char *, int);
int binsearch(char *, struct key *, int);

/* count C keywords */
int main(int argc, char *argv[])
{
    int n;
    char word[MAXWORD];

    while (mgetword(word, MAXWORD) != EOF) 
        if (isalpha(word[0])) 
            if ((n = binsearch(word, keytab, NKEYS)) >= 0)
                keytab[n].count++;
            for (n = 0; n < NKEYS; n++)
                if (keytab[n].count > 0)
                    printf("%4d %s\n", keytab[n].count, keytab[n].word);
                return 0;
            
}

/* binsearch: find word in tab[0]...tab[n-1] */
int binsearch(char *word, struct key tab[], int n)
{
    int cond;
    int low, high, mid;
    low = 0;
    high = n - 1;
    while (low <= high) {
        mid = (low+high) / 2;
        if ((cond = strcmp(word, tab[mid].word)) < 0)
            high = mid - 1;
        else if (cond > 0)
            low = mid + 1;
        else
            return mid;
    }
    return -1;

}

/* getword: get next word or character from input */
int mgetword(char *word, int lim)
{
    int c, getch(void);
    void ungetch(int);
    char *w = word;
    while (isspace(c = getch()))
        ;
    if (c != EOF)
        *w++ = c;
    if (!isalpha(c)) {
        *w = '\0';
        return c;
    }
    for ( ; --lim > 0; w++)
        if (!isalnum(*w = getch())) {
            ungetch(*w);
            break;
        }
        *w = '\0';
        return word[0];
}

#define BUFSIZE  100

char buf[BUFSIZE];  /* buffer for ungetch */
int bufp = 0;       /* next free position in buf */

int getch(void)     /* get a (possibly pushed back) character */
{
    return ( bufp > 0)? buf[--bufp] : getchar();
}

void ungetch(int c)     /* push a character back on input */
{
    if(bufp >= BUFSIZE)
        printf("ungetch: too many characters \n");
    else
        buf[bufp++] = c;
}
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