TCPL 习题集 第四章

4-12.c

#include <stdio.h>

char s[100];
int i = 0;

void itoa(int);

void itoa(int d) {
    int tmp;
    if(d == 0) {
        for(int j = 0, k = i - 1; j < k; j++, k--) {
            tmp = s[j];
            s[j] = s[k];
            s[k] = tmp;
        }
        s[i] = '\0';
        printf("%s\n", s);
    } else {
        s[i++] = d % 10 + '0';
        itoa(d /= 10);
    }
}

int main() {
    itoa(523123);
}

4-2.c

//由字符串转为数字，支持科学表示法

#include <stdio.h>

double atof(char[]);
void skipSpace(char[]);
double getE(char[], int);
int isspace(char);
int isdigit(char);

int main() {
    char s[] = "12.133e12.f";
    printf("%f\n", atof(s));
}

double val, power;
int i, sign;

double atof(char s[]) {
    skipSpace(s);
    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;
    }

    double e = getE(s, i);

    return sign * val * e / power;
}

void skipSpace(char s[]) {
    for(i = 0; isspace(s[i]); i++)
        ;
}

double getE(char s[], int i) {
    int powerSign;
    int num = 0;
    double e = 1.0;
    if(s[i] == 'e' || s[i] == 'E')
        i++;
    
    if(s[i] == '+' || s[i] == '-') {
        powerSign = s[i] == '-' ? -1 : 1;
        i++;
    } else {
        powerSign = 1;
    }
    while(isdigit(s[i])) {
        num = 10 * num + (s[i] - '0');
        i++;
    }
    for(i = 0; i < num; i++) {
        if(powerSign > 0) {
            e *= 10.0;
        } else {
            e /= 10.0;
        }
    }
    return e;
}

int isspace(char c) {
    return (c == ' ' || c == '\t' || c == '\n') ? 1 : 0;
}

int isdigit(char c) {
    return (c >= '0' && c <= '9') ? 1 : 0;
}

4-3.c

#include <stdio.h>
#include <stdlib.h>

#define MAXOP 100
#define NUMBER '0'
#define MAXVAL 100
#define BUFSIZE 100


int getop(char[]);
int getch();
void ungetch(int);
void push(double);
double pop();
int isdigit(char);

int sp = 0;
double val[MAXVAL];
char buf[BUFSIZE];
int bufp = 0;

void push(double f) {
    if(sp < MAXVAL)
        val[sp++] = f;
    else
        printf("error: stack full, can't push %g\n", f);
}

double pop() {
    if(sp > 0)
        return val[--sp];
    else {
        printf("error: stack empty\n");
        return 0.0;
    }
}

int getch() {
    return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c) {
    if(bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}

int getop(char s[]) {
    int i = 0, c, n;
    while((s[0] = c = getch()) == ' ' || c == '\t');
    s[1] = '\0';
    if(c == '-') {
        n = getch();        
        if(!isdigit(n) && n != '.') {
            ungetch(n);
            return c;
        } else {
            s[i++] = c;
            c = s[i] = n;
        }
    } else if(!isdigit(c) && c != '.' && c != '-')
        return c;    
    
    if(isdigit(c))
        while(isdigit(s[++i] = c = getch()));
    if(c == '.')
        while(isdigit(s[++i] = c = getch()));
    s[i] = '\0';
    if(c != EOF)
        ungetch(c);
    return NUMBER;
}

int main() {
    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 '-':
            op2 = pop();
            push(pop() - op2);
            break;
        case '*':
            push(pop() * pop());
            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((int)pop() % (int)op2);
            } else
                printf("error: zero divisor\n");
            break;
        case '\n':
            printf("\t%.8g\n", pop());
            break;
        default:
            printf("error: unknown command %s\n", s);
            break;
        }
    }
    return 0;
}

int isdigit(char c) {
    return (c >= '0' && c <= '9') ? 1 : 0;
}