example

#include<stdio.h>#include<string.h>#include<ctype.h>#define MAXWORD 100#define NKEYS (sizeof keytab/sizeof keytab[0])#define BUFSIZE 100char buf[BUFSIZE];int bufp=0;struct key {        char *word;        int count;} keytab[]={        {"auto",0},        {"break",0},        {"case",0},        {"char",0},        {"const",0},        {"continue",0},        {"default",0},        {"do",0},        {"double",0},        {"else",0},        {"enum",0},        {"extern",0},        {"float",0},        {"for",0},        {"goto",0},        {"if",0},        {"int",0},        {"struct",0},        {"long",0},        {"register",0},        {"return",0},        {"short",0},        {"signed",0},        {"sizeof",0},        {"static",0},        {"switch",0},        {"typedef",0},        {"union",0},        {"unsigned",0},        {"void",0},        {"volatile",0},        {"while",0}};int getword(char *,int);int binsearch(char *,struct key *,int);main(){        int n;        char word[MAXWORD];        while(getword(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;}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;}int getword(char *word,int lim){        int c;        char *w=word;        int getch(void);        void ungetch(int);        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];}int getch(void){return (bufp>0) ? buf[--bufp] : getchar();}void ungetch(int c){        if(bufp>=BUFSIZE)                printf("ungetch:too many characters\n");        else                buf[bufp++]=c;}