《The C Programming Language》答案（第一章）

P1

#include 
   
    main(){
     printf("hello, world\n");}

P2

warning: unknown escape sequence: '\c'

P3

#include 
   
    main(){
     float fahr,celsius;  float lower,upper,step;  lower = 0;  upper = 300;  step = 20;  fahr = lower;  printf("fahr celsius\n");  while(fahr<=upper){
       celsius = (5.0/9.0)*(fahr-32.0);    printf("%3.0f %6.1f\n",fahr,celsius);    fahr = fahr+step;  }}

P4

#include 
   
    main(){
     float fahr,celsius;  float lower,upper,step;  lower = 0;  upper = 300;  step = 20;  celsius = lower;  printf("celsius fahr\n");  while(celsius<=upper){
       //celsius = (5.0/9.0)*(fahr-32.0);    fahr=(9.0/5.0)*celsius+32.0;    printf("%3.0f %6.1f\n",celsius,fahr);    celsius = celsius+step;  }}

P5

#include 
   
    main(){
     float fahr,celsius;  float lower,upper,step;  lower = 0;  upper = 300;  step = 20;  fahr = upper;  printf("fahr celsius\n");  for(fahr;fahr>=lower;fahr-=step){
       celsius = (5.0/9.0)*(fahr-32.0);    //fahr=(9.0/5.0)*celsius+32.0;    printf("%3.0f %6.1f\n",fahr,celsius);    //celsius = celsius+step;  }}

P6

#include 
   
    //the answer is 1main(){
     printf("%d\n",getchar()!=EOF);}

P7

#include 
   
    //the answer is -1main(){
     printf("%d\n",EOF);}

P8

#include 
   
    //press ctrl+Z in windows, ctrl+D in Linuxmain(){
     int tmp,emptyCount,tableCount,lineCount;  emptyCount=0;  tableCount=0;  lineCount=0;  while(1){
       tmp=getchar();    if(tmp==EOF)      break;    if(tmp==' ')      ++emptyCount;    if(tmp=='\t')      ++tableCount;    if(tmp=='\n')      ++lineCount;  }  printf("Empties: %d\nTables: %d\nLines: %d\n",emptyCount,tableCount,lineCount);}

P9

#include 
   
    //ctrl+Z in windows, ctrl+D in Linux to end the inputmain(void){
       int c, blank_flag;    blank_flag = 0;    while (1){
         c = getchar();      if(c==EOF)        break;      if (c == ' ') {
             if (!blank_flag) {
                 blank_flag = 1;              putchar(c);          }      } else {
             blank_flag = 0;          putchar(c);      }    }}

P10

#include 
   
    //ctrl+Z in windows, ctrl+D in Linux to end the input.main(void){
       int c;    while (1){
         c = getchar();      if(c==EOF)        break;      if (c == '\t')          printf("\\t");      else if (c == '\b')          printf("\\b");      else if (c == '\\')          printf("\\\\");      else          printf("%c", c);    }}

P11

行首空格，空行

P12

#include 
   
    //ctrl+Z in windows, ctrl+D in Linux to end the inputint main(void){
       int c, lineflag;    lineflag = 0;    while (1){
         c = getchar();      if(c==EOF)        break;      if (c == ' ' || c == '\t' || c == '\n') {
             if (!lineflag) {
                 putchar('\n');              lineflag = 1;          }      } else {
             putchar(c);          lineflag = 0;      }    }    return 0;}

P13

#include 
   
    #define MAX_LENGTH 15#define IN_WORD 1#define OUT_WORD 0int main(void){
       int c, word_in_flag;    int word_length[MAX_LENGTH + 1];    int l;    int i, j;    unsigned int max_count;    for (i = 0; i <= MAX_LENGTH; ++i)        word_length[i] = 0;    word_in_flag = OUT_WORD;    while (1) {
           c = getchar();        if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) {
               if (word_in_flag == OUT_WORD) {
                   l = 0;                word_in_flag = IN_WORD;            }            ++l;        } else {
               if (word_in_flag == IN_WORD) {
                   if (l <= MAX_LENGTH)                    ++word_length[l - 1];                else                    ++word_length[MAX_LENGTH];                word_in_flag = OUT_WORD;            }            if (c == EOF)                break;        }    }//horizon    for (i = 0; i <= MAX_LENGTH; ++i) {
           if (i != MAX_LENGTH)            printf("     %2d | ", i + 1);        else            printf("    >%2d | ", MAX_LENGTH);        for (j = 0; j < word_length[i]; ++j)            putchar('+');        putchar('\n');    }//vertical    max_count = 0;    for (i = 0; i <= MAX_LENGTH; ++i)        if (word_length[i] > max_count)            max_count = word_length[i];    for (i = 0; i < max_count; ++i) {
           printf("  %2u | ", max_count - i);        for (j = 0; j <= MAX_LENGTH; ++j)            if (word_length[j] >= max_count - i)                printf("  +");            else                printf("   ");        printf("\n");    }    printf(" ------");    for (i = 0; i <= MAX_LENGTH; ++i)        printf("---");    printf("--\n");    printf("       ");    for (i = 0; i < MAX_LENGTH;)        printf(" %2u", ++i);    printf(" >%2u", MAX_LENGTH);    printf("\n");    return 0;}

P14

#include 
   
    #define NUM_CHARS 128#define IN_WORD 1#define OUT_WORD 0//ctrl+Z in windows, ctrl+D in Linux to finish inputint main(void){
       int c;    int char_frequencies[NUM_CHARS + 1];    int i;    for (i = 0; i <= NUM_CHARS; ++i)        char_frequencies[i] = 0;    while ((c = getchar()) != EOF)        ++char_frequencies[c];    printf("\n ASCII | Count\n");    for (i = 0; i <= NUM_CHARS; ++i)         if (char_frequencies[i] > 0)            printf(" %5d : %5d\n", i, char_frequencies[i]);    return 0;}

P15

略

P16

#include 
   
    #define MAXLINE 1000 /* maximum input line length */int get_line(char line[], int maxline);void copy(char to[], char from[]);/* print the longest input line */int main(void){
       int len; /* current line length */    int max; /* maximum length seen so far */    char line[MAXLINE]; /* current input line */    char longest[MAXLINE]; /* longest line saved here */    max = 0;    while ((len = get_line(line, MAXLINE)) > 0)        if (len > max) {
               max = len;            copy(longest, line);        }    if (max > 0) {
           printf("The longest line is:\n");        printf("%s\n", longest);        printf("The length of it is %d.\n", max);    }    return 0;}/* get_line: read a line into s, return length */int get_line(char s[], int lim){
       int c, i, l;    for (i = 0, l = 0; (c = getchar()) != EOF && c != '\n'; ++i) {
           if (i < lim - 1)            s[l++] = c;    }    if (c == '\n') {
           if (l < lim - 1)            s[l++] = c;        ++i;    }       s[l] = '\0';    return i;}/* copy: copy 'from' into 'to'; assume to is big enough */void copy(char to[], char from[]){
       int i;    i = 0;    while ((to[i] = from[i]) != '\0')        ++i;}

P17

#include 
   
    #define MAXLINE 1000#define MAXLENGTH 10int get_line(char s[],int lim){
     int c,i,l;  for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i){
       if(i
    
     0)    if(len>MAXLENGTH)      printf("%s\n",line);  return 0;}

P18

#include 
   
    #define MAXLINE 1000#define MAXLENGTH 10int get_line(char s[],int lim){
     int c,i,l;  for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i){
       if(i
    
     0){
       if(len==1&&line[0]=='\n')      continue;    printf("%s\n",line);  }  return 0;}

P19

#include 
   
    #define MAXLINE 1000#define MAXLENGTH 10int get_line(char s[],int lim){
     int c,i,l;  for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i){
       if(i
    
     0){
       reverse(line);    printf("%s\n",line);  }  return 0;}

P20

#include 
   
    #define MAXLINE 1000#define TAB_WIDTH 4int getchars(char s[],int lim){
     int c,i,l;  for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i)    if(i

P21

#include 
   
    #define MAXLINE 1000#define TAB_WIDTH 8int getchars(char s[],int lim){
     int c,i,l;  for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i)    if(i

P22

#include 
   
    #define MAXLINE 1000#define TAB_WIDTH 8#define LINE_WIDTH 10int getchars(char s[],int lim){
     int c,i,l;  for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i)    if(i
    
     =linewidth){
           s2[l++]='\n';        w=0;        i=k;      }else{
           s2[l++]='\t';        w+=tabwidth;      }    }else{
         s2[l++]=c;      if(w+1==linewidth){
           s2[l++]='\n';        w=0;      }else{
           k=i;        ++w;      }    }    ++i;  }  s2[l++]='\0';}int main(){
     char s1[MAXLINE];  char s2[MAXLINE];  while(getchars(s1,MAXLINE)==0)    ;  fold(s1,s2,LINE_WIDTH,TAB_WIDTH);  printf("%s\n",s2);  return 0;}

P23

#include 
   
    #define MAXLENGTH 5000//ctrl+Z in windows, ctrl+D in Linux to end the inputint _getline(char s[], int max){
       int c, i, l;    for (i = 0, l = 0; (c = getchar()) != EOF; ++i)        if (i < max - 1)            s[l++] = c;    s[l] = '\0';    return l;}int main(void){
       int len, i;    char s[MAXLENGTH];    while ((len = _getline(s, MAXLENGTH)) > 0) {
           i = 0;        while (s[i] != '\0') {
               if (s[i] == '/' && s[i+1] == '/') {
                   i += 2;                while (s[i] != '\n' && s[i] != '\0')                    ++i;            } else if (s[i] == '/' && s[i+1] == '*') {
                   i += 2;                while (s[i] != '\0' && s[i+1] != '\0' && (s[i] != '*' || s[i+1] != '/'))                    ++i;                if (s[i] != '\0' && s[i+1] == '\0')                    ++i;                if (s[i] == '*')                    i += 2;            } else if (s[i] == '\"') {
                   putchar('\"');                ++i;                while (s[i] != '\0' && (s[i-1] == '\\' || s[i] != '\"'))                    putchar(s[i++]);            } else {
                   putchar(s[i++]);            }        }    }        return 0;}