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《The C Programming Language》答案（第四章）
阅读量：4169 次
发布时间：2019-05-26

本文共 23335 字，大约阅读时间需要 77 分钟。

《The C Programming Language》答案（第四章）

P1

#include 
   
    #include 
    
     #define MAXLINE 1024int getchars(char s[],int max){
       int c, i, l;    for (i = 0, l = 0; (c = getchar()) != EOF && c != '\n'; ++i)        if (i < max - 1)            s[l++] = c;    s[l] = '\0';    return l;}int strindex(char s[], char t[]){
       int sl, tl;    int i, j, k;    int c;    sl = strlen(s);    tl = strlen(t);    i = sl - tl;    while (i >= 0) {
           for (j = i, k = 0; t[k] != '\0' && s[j] == t[k]; ++j, ++k)            ;        if (k > 0 && t[k] == '\0')            return i;        --i;    }    return -1;}int main(){
       char src[MAXLINE];    char ptrn[MAXLINE];    printf("Please Enter: \n");    while(getchars(ptrn,MAXLINE)==0)        ;    printf("The rightmost index is: %d\n",strindex(src,ptrn));    return 0;}

P2

#include 
   
    #include 
    
     #define MAXLINE 1024int getchars(char s[], int max){
       int c, i, l;    for (i = 0, l = 0; (c = getchar()) != EOF && c != '\n'; ++i)        if (i < max - 1)            s[l++] = c;    s[l] = '\0';    return l;}double atof(char s[]){
       double val, power, base, epower;    int i, sign, exponent;    for (i = 0; isspace(s[i]); i++) /* skip white space */        ;    sign = (s[i] == '-') ? -1 : 1;    if (s[i] == '+' || s[i] == '-')        i++;    for (val = 0.0; isdigit(s[i]); i++)        val = 10.0 * val + (s[i] - '0');    if (s[i] == '.')        i++;    for (power = 1.0; isdigit(s[i]); i++) {
           val = 10.0 * val + (s[i] - '0');        power *= 10;    }    epower = 1;    if (s[i] == 'e' || s[i] == 'E') {
           i++;        base = s[i] == '-' ? 0.1 : 10.0;        if (s[i] == '-' || s[i] == '+')            i++;        for (exponent = 0; isdigit(s[i]); i++) {
               exponent = 10 * exponent + (s[i] - '0');        }        while (exponent-- > 0)            epower *= base;    }    return sign * val / power * epower;}int main(void){
       char s[MAXLINE];    printf("Enter a number:\n");    while(getchars(s,MAXLINE)==0)        ;    printf("The number is %lf\n",atof(s));    return 0;}

P3

#include 
   
    #include 
    
     #include 
     
      #define MAXLINE 1024#define MAXOP 100#define NUMBER '0'int getop(char []);void push(double);double pop(void);int main(void){
       int type;    double op2;    char s[MAXOP];    while ((type = getop(s)) != EOF) {
           switch (type) {
           case NUMBER:            push(atof(s));            break;        case '+':            push(pop() + pop());            break;        case '*':            push(pop() * pop());            break;        case '-':            op2 = pop();            push(pop() - op2);            break;        case '/':            op2 = pop();            if (op2 != 0.0)                push(pop() / op2);            else                printf("error: zero divisor\n");            break;        case '%':            op2 = pop();            if (op2 != 0.0)                push(fmod(pop(), op2));            else                printf("error: zero divisor\n");            break;        case '\n':            printf("= %g\n", pop());            break;        default:            printf("error: unknown command %s\n", s);        break;        }    }    return 0;}#define MAXVAL 100 /* maximum depth of val stack */int sp = 0; /* next free stack position */double val[MAXVAL]; /* value stack *//* push: push f onto value stack */void push(double f){
       if (sp < MAXVAL)        val[sp++] = f;    else        printf("error: stack full, can't push %g\n", f);}/* pop: pop and return top value from stack */double pop(void){
       if (sp > 0)        return val[--sp];    else {
           printf("error: stack empty\n");        return 0.0;    }}#include 
      
       int getch(void);void ungetch(int);/* getop: get next character or numeric operand */int getop(char s[]){
       int i, c, c2;    while ((s[0] = c = getch()) == ' ' || c == '\t')        ;    s[1] = '\0';        if (!isdigit(c) && c != '.' && c != '-')        return c; /* not a number */    i = 0;    if (c == '-') {
           c2 = getch();        if (c2 != EOF)            ungetch(c2);        if (!isdigit(c2) && c2 != '.')            return c;    }    if (isdigit(c) || c == '-') /* collect integer part */        while (isdigit(s[++i] = c = getch()))            ;    if (c == '.') /* collect fraction part */        while (isdigit(s[++i] = c = getch()))            ;    s[i] = '\0';    if (c != EOF)        ungetch(c);    return NUMBER;}#define BUFSIZE 100char 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 character back on input */{
       if (bufp >= BUFSIZE)        printf("ungetch: too many characters\n");    else        buf[bufp++] = c;}

P4

#include 
   
    #include 
    
     #include 
     
      #define MAXLINE 1024#define MAXOP 100#define NUMBER '0'int getop(char []);void push(double);double pop();void printtop();void duplicate();void swap();void clear();int main(void){
       push(114.514);    push(1919.810);    duplicate();    printtop();    swap();    clear();    return 0;}#define MAXVAL 100 /* maximum depth of val stack */int sp = 0; /* next free stack position */double val[MAXVAL]; /* value stack *//* push: push f onto value stack */void push(double f){
       if (sp < MAXVAL)        val[sp++] = f;    else        printf("error: stack full, can't push %g\n", f);}/* pop: pop and return top value from stack */double pop(void){
       if (sp > 0)        return val[--sp];    else {
           printf("error: stack empty\n");        return 0.0;    }}/* printtop: print the top element of the stack */void printtop(void){
       if (sp > 0)        printf("%g\n", val[sp - 1]);    else        printf("error: stack empty\n");}/* duplicate:  duplicate the top element of the stack */void duplicate(void){
       double top = pop();    push(top);    push(top);}/* swap:  swap the top two elements of the stack */void swap(void){
       double top1 = pop();    double top2 = pop();    push(top1);    push(top2);}/* clear: clear stack */void clear(void){
       sp = 0;}

P5

#include 
   
    #include 
    
     #include 
     
      #define MAXLINE 1024#define MAXOP 100#define NUMBER '0'#define MATHLIB '1'int getop(char []);void push(double);double pop();int main(void){
       int type;    double op2;    char s[MAXOP];    while ((type = getop(s)) != EOF) {
           switch (type) {
           case NUMBER:            push(atof(s));            break;        case MATHLIB:            if (strcmp(s, "sin") == 0)                push(sin(pop()));            else if (strcmp(s, "cos") == 0)                push(cos(pop()));            else if (strcmp(s, "pow") == 0) {
                   op2 = pop();                push(pow(pop(), op2));            } else                printf("error: unknown command %s\n", s);            break;        case '+':            push(pop() + pop());            break;        case '*':            push(pop() * pop());            break;        case '-':            op2 = pop();            push(pop() - op2);            break;        case '/':            op2 = pop();            if (op2 != 0.0)                push(pop() / op2);            else                printf("error: zero divisor\n");            break;        case '%':            op2 = pop();            if (op2 != 0.0)                push(fmod(pop(), op2));            else                printf("error: zero divisor\n");            break;        case '\n':            printf("= %g\n", pop());            break;        default:            printf("error: unknown command %s\n", s);        break;        }    }    return 0;}#define MAXVAL 100 /* maximum depth of val stack */int sp = 0; /* next free stack position */double val[MAXVAL]; /* value stack *//* push: push f onto value stack */void push(double f){
       if (sp < MAXVAL)        val[sp++] = f;    else        printf("error: stack full, can't push %g\n", f);}/* pop: pop and return top value from stack */double pop(void){
       if (sp > 0)        return val[--sp];    else {
           printf("error: stack empty\n");        return 0.0;    }}#include 
      
       int getch(void);void ungetch(int);/* getop: get next character or numeric operand */int getop(char s[]){
       int i, c, c2;    while ((s[0] = c = getch()) == ' ' || c == '\t')        ;    s[1] = '\0';    i = 0;    if (isalpha(c)) {
           while (isalpha(s[++i] = c = getch()))            ;        s[i] = '\0';        if (c != EOF)            ungetch(c);        return MATHLIB;    }    if (!isdigit(c) && c != '.' && c != '-')        return c; /* not a number */    if (c == '-') {
           c2 = getch();        if (c2 != EOF)            ungetch(c2);        if (!isdigit(c2) && c2 != '.')            return c;    }    if (isdigit(c) || c == '-') /* collect integer part */        while (isdigit(s[++i] = c = getch()))            ;    if (c == '.') /* collect fraction part */        while (isdigit(s[++i] = c = getch()))            ;    s[i] = '\0';    if (c != EOF)        ungetch(c);    return NUMBER;}#define BUFSIZE 100char 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 character back on input */{
       if (bufp >= BUFSIZE)        printf("ungetch: too many characters\n");    else        buf[bufp++] = c;}

P6

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #define MAXLINE 1024#define MAXOP 100#define NUMBER '0'#define MATHLIB '1'#define VARIABLE '2'int getop(char []);void push(double);double pop(void);double vars[26];double last;int main(void){
       int type, v;    double op2;    char s[MAXOP];    while ((type = getop(s)) != EOF) {
           switch (type) {
           case NUMBER:            push(atof(s));            break;        case MATHLIB:            if (strcmp(s, "sin") == 0)                push(sin(pop()));            else if (strcmp(s, "cos") == 0)                push(cos(pop()));            else if (strcmp(s, "pow") == 0) {
                   op2 = pop();                push(pow(pop(), op2));            } else if (strcmp(s, "last") == 0) {
                   printf("the most recently printed value is %g\n", last);            } else                printf("error: unknown command %s\n", s);            break;        case '+':            push(pop() + pop());            break;        case '*':            push(pop() * pop());            break;        case '-':            op2 = pop();            push(pop() - op2);            break;        case '/':            op2 = pop();            if (op2 != 0.0)                push(pop() / op2);            else                printf("error: zero divisor\n");            break;        case '%':            op2 = pop();            if (op2 != 0.0)                push(fmod(pop(), op2));            else                printf("error: zero divisor\n");            break;        case VARIABLE:            v = tolower(s[0]);            last = vars[v - 'a'] = pop();            push(last);            break;        case '\n':            printf("= %g\n", pop());            break;        default:            printf("error: unknown command %s\n", s);        break;        }    }    return 0;}#define MAXVAL 100 /* maximum depth of val stack */int sp = 0; /* next free stack position */double val[MAXVAL]; /* value stack *//* push: push f onto value stack */void push(double f){
       if (sp < MAXVAL)        val[sp++] = f;    else        printf("error: stack full, can't push %g\n", f);}/* pop: pop and return top value from stack */double pop(void){
       if (sp > 0)        return val[--sp];    else {
           printf("error: stack empty\n");        return 0.0;    }}#include 
        
         int getch(void);void ungetch(int);/* getop: get next character or numeric operand */int getop(char s[]){ int i, c, c2; while ((s[0] = c = getch()) == ' ' || c == '\t') ; s[1] = '\0'; i = 0; if (isalpha(c)) { while (isalpha(s[++i] = c = getch())) ; s[i] = '\0'; if (c != EOF) ungetch(c); return MATHLIB; } if (!isdigit(c) && c != '.' && c != '-') { if (c == '=') { if (isalpha(c2 = getch())) { s[0] = c2; return VARIABLE; } else if (c2 != EOF) { ungetch(c2); } } return c; /* not a number */ } if (c == '-') { c2 = getch(); if (c2 != EOF) ungetch(c2); if (!isdigit(c2) && c2 != '.') return c; } if (isdigit(c) || c == '-') /* collect integer part */ while (isdigit(s[++i] = c = getch())) ; if (c == '.') /* collect fraction part */ while (isdigit(s[++i] = c = getch())) ; s[i] = '\0'; if (c != EOF) ungetch(c); return NUMBER;}#define BUFSIZE 100char 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 character back on input */{ if (bufp >= BUFSIZE) printf("ungetch: too many characters\n"); else buf[bufp++] = c;}

P7

#include 
   
    #include 
    
     int getch();void ungetch(int);void ungets(char s[]);int main(void){
       ungets("testring");    putchar(getch());    putchar(getch());    putchar(getch());    putchar(getch());    putchar(getch());    putchar(getch());    putchar(getch());    putchar(getch());    return 0;}#define BUFSIZE 100char 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 character back on input */{
       if (bufp >= BUFSIZE)        printf("ungetch: too many characters\n");    else        buf[bufp++] = c;}void ungets(char s[]){
         int l = strlen(s);  while (l)    ungetch(s[--l]);}

P8

#include 
   
    int getch();void ungetch(int);int main(void){
       ungetch('a');    ungetch('t');    putchar(getch());    return 0;}int buf = -1; /* buffer for ungetch */int getch(void) /* get a (possibly pushed-back) character */{
       int b = buf;    if (b > -1) {
           buf = -1;        return b;    }    return getchar();}void ungetch(int c) /* push character back on input */{
       buf = c;}

P9

#include 
   
    int getch();void ungetch(int);int main(void){
       ungetch('t');    ungetch(EOF);    putchar(getch());    return 0;}#define BUFSIZE 100char 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 character back on input */{
       if (bufp >= BUFSIZE)        printf("ungetch: too many characters\n");    else if (c != EOF)        buf[bufp++] = c;}

P10

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #define MAXLINE 1024#define MAXOP 100#define NUMBER '0'#define MATHLIB '1'#define VARIABLE '2'int get_line(char line[],int limit);char line[MAXLINE];int linep = 0;int getop(char []);void push(double);double pop();double vars[26];double last;int main(void){
       int type, v;    double op2;    char s[MAXOP];    while (get_line(line, MAXLINE) > 0) {
           linep = 0;           while ((type = getop(s)) != '\0') {
               switch (type) {
               case NUMBER:                push(atof(s));                break;            case MATHLIB:                if (strcmp(s, "sin") == 0)                    push(sin(pop()));                else if (strcmp(s, "cos") == 0)                    push(cos(pop()));                else if (strcmp(s, "pow") == 0) {
                       op2 = pop();                    push(pow(pop(), op2));                } else if (strcmp(s, "last") == 0) {
                       printf("the most recently printed value is %g\n", last);                } else                    printf("error: unknown command %s\n", s);                break;            case '+':                push(pop() + pop());                break;            case '*':                push(pop() * pop());                break;            case '-':                op2 = pop();                push(pop() - op2);                break;            case '/':                op2 = pop();                if (op2 != 0.0)                    push(pop() / op2);                else                    printf("error: zero divisor\n");                break;            case '%':                op2 = pop();                if (op2 != 0.0)                    push(fmod(pop(), op2));                else                    printf("error: zero divisor\n");                break;            case VARIABLE:                v = tolower(s[0]);                last = vars[v - 'a'] = pop();                push(last);                break;            case '\n':                printf("= %g\n", pop());                break;            default:                printf("error: unknown command %s\n", s);            break;            }        }    }    return 0;}#define MAXVAL 100 /* maximum depth of val stack */int sp = 0; /* next free stack position */double val[MAXVAL]; /* value stack *//* push: push f onto value stack */void push(double f){
       if (sp < MAXVAL)        val[sp++] = f;    else        printf("error: stack full, can't push %g\n", f);}/* pop: pop and return top value from stack */double pop(void){
       if (sp > 0)        return val[--sp];    else {
           printf("error: stack empty\n");        return 0.0;    }}#include 
        
         /* getop: get next character or numeric operand */int getop(char s[]){ int i, c, c2; while ((s[0] = c = line[linep++]) == ' ' || c == '\t') ; s[1] = '\0'; i = 0; if (isalpha(c)) { while (isalpha(s[++i] = c = line[linep++])) ; s[i] = '\0'; if (c != '\0') --linep; return MATHLIB; } if (!isdigit(c) && c != '.' && c != '-') { if (c == '=') { if (isalpha(c2 = line[linep++])) { s[0] = c2; return VARIABLE; } else if (c2 != '\0') { --linep; } } return c; /* not a number */ } if (c == '-') { c2 = line[linep++]; if (c2 != '\0') --linep; if (!isdigit(c2) && c2 != '.') return c; } if (isdigit(c) || c == '-') /* collect integer part */ while (isdigit(s[++i] = c = line[linep++])) ; if (c == '.') /* collect fraction part */ while (isdigit(s[++i] = c = line[linep++])) ; s[i] = '\0'; if (c != '\0') --linep; return NUMBER;}int get_line(char s[], int max){ int c, i, l; for (i = 0, l = 0; (c = getchar()) != EOF && c != '\n'; ++i) if (i < max - 1) s[l++] = c; if (c == '\n') s[l++] = c; s[l] = '\0'; return l;}

P11

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #define MAXLINE 1024#define MAXOP 100#define NUMBER '0'#define MATHLIB '1'#define VARIABLE '2'int getop(char []);void push(double);double pop();double vars[26];double last;int main(void){
       int type, v;    double op2;    char s[MAXOP];    while ((type = getop(s)) != EOF) {
           switch (type) {
           case NUMBER:            push(atof(s));            break;        case MATHLIB:            if (strcmp(s, "sin") == 0)                push(sin(pop()));            else if (strcmp(s, "cos") == 0)                push(cos(pop()));            else if (strcmp(s, "pow") == 0) {
                   op2 = pop();                push(pow(pop(), op2));            } else if (strcmp(s, "last") == 0) {
                   printf("the most recently printed value is %g\n", last);            } else                printf("error: unknown command %s\n", s);            break;        case '+':            push(pop() + pop());            break;        case '*':            push(pop() * pop());            break;        case '-':            op2 = pop();            push(pop() - op2);            break;        case '/':            op2 = pop();            if (op2 != 0.0)                push(pop() / op2);            else                printf("error: zero divisor\n");            break;        case '%':            op2 = pop();            if (op2 != 0.0)                push(fmod(pop(), op2));            else                printf("error: zero divisor\n");            break;        case VARIABLE:            v = tolower(s[0]);            last = vars[v - 'a'] = pop();            push(last);            break;        case '\n':            printf("= %g\n", pop());            break;        default:            printf("error: unknown command %s\n", s);        break;        }    }    return 0;}#define MAXVAL 100 /* maximum depth of val stack */int sp = 0; /* next free stack position */double val[MAXVAL]; /* value stack *//* push: push f onto value stack */void push(double f){
       if (sp < MAXVAL)        val[sp++] = f;    else        printf("error: stack full, can't push %g\n", f);}/* pop: pop and return top value from stack */double pop(void){
       if (sp > 0)        return val[--sp];    else {
           printf("error: stack empty\n");        return 0.0;    }}#include 
        
         int getch(void);/* getop: get next character or numeric operand */int getop(char s[]){ static int buf = EOF; int i, c, c2; while ((s[0] = c = (buf == EOF ? getch() : buf)) == ' ' || c == '\t') buf = EOF; buf = EOF; s[1] = '\0'; i = 0; if (isalpha(c)) { while (isalpha(s[++i] = c = (buf == EOF ? getch() : buf))) buf = EOF; buf = EOF; s[i] = '\0'; if (c != EOF) buf = c; return MATHLIB; } if (!isdigit(c) && c != '.' && c != '-') { if (c == '=') { c2 = (buf == EOF ? getch() : buf); buf = EOF; if (isalpha(c2)) { s[0] = c2; return VARIABLE; } else if (c2 != EOF) { buf = c2; } } return c; /* not a number */ } if (c == '-') { c2 = (buf == EOF ? getch() : buf); buf = EOF; if (c2 != EOF) buf = c2; if (!isdigit(c2) && c2 != '.') return c; } if (isdigit(c) || c == '-') /* collect integer part */ while (isdigit(s[++i] = c = (buf == EOF ? getch() : buf))) { buf = EOF; } buf = EOF; if (c == '.') /* collect fraction part */ while (isdigit(s[++i] = c = (buf == EOF ? getch() : buf))) buf = EOF; buf = EOF; s[i] = '\0'; if (c != EOF) buf = c; return NUMBER;}int getch(void) /* get a (possibly pushed-back) character */{ return getchar();}

P12

#include 
   
    #include 
    
     #include 
     
      #define MAXLINE 1024void itoa(int n,char s[]);void itoaR(int n,char s[]);int main(void){
       char s[MAXLINE];    itoa(INT_MIN, s);    printf("%d ---> %s.\n", INT_MIN, s);    return 0;}void itoa(int n, char s[]){
       s[0] = '\0';    itoaR(n, s);}void itoaR(int n, char s[]){
       int remainder, l;    if (n / 10)        itoa(n / 10, s);    l = strlen(s);    if (n / 10 == 0 && n < 0)        s[l++] = '-';    remainder = n % 10;    s[l++] = ((n < 0) ? -remainder : remainder) + '0';    s[l++] = '\0';}

P13

#include 
   
    #include 
    
     #define MAXLINE 1024int getchars(char line[],int max);void reverse(char s[]){
       reverseR(s,0,strlen(s)-1);}void reverseR(char s[],int i,int j){
       int tmp;    tmp = s[i];    s[i] = s[j];    s[j] = tmp;    if(i

P14

#include 
   
    #include 
    
     #define swap(t,x,y) {t tmp;tmp=x;x=y;y=tmp;}int main(){
       int a=114;    int b=514;    printf("Before swap, a=%d,b=%d\n",a,b);    swap(int,a,b)    printf("After swap, a=%d,b=%d\n",a,b);}

第四章 完

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