TCPL 习题集 第五章

5-2.c

//部分程序来自于上一章节
//getfloat：将字符串转换成 float

#include <stdio.h>
#include <ctype.h>
#include "calc.h"

int getch(void);
void ungetch(int);
int getfloat(double *);

int getfloat(double *d) {
    int c, sign;
    double power = 10.0;
    while(isspace(c = getch()))
        ;
    if(!isdigit(c) && c != '-' && c != '+' && c != EOF && c != '.') {
        ungetch(c);
        return 0;
    }
    sign = (c == '-') ? -1 : 1;
    if(c == '+' || c == '-')
        c = getch();
    for(*d = 0.0; isdigit(c); c = getch()) {
        *d = 10 * *d + (c - '0');
    }
    if(c == '.') {
        c = getch();
        for(; isdigit(c); c = getch()) {
            *d += (c - '0') / power;
            power *= 10.0;
        }
    }
    *d *= sign;
    if(c != EOF)
        ungetch(c);
    return c;
}

int main(){
    double d = 0.0;
    printf("Return = %g\n", getfloat(&d));
    printf("Result = %.12g\n", d);
}

5-3.c

//将字符串 t 拼接到 s 后面

#include <stdio.h>

void strcat(char*, char*);

void strcat(char *s, char *t) {
    while(*s++);
    *--s;
    while(*s++ = *t++);
}

int main(){
    char t[] = "0123456789";
    char s[20] = "abc";
    strcat(s, t);
    printf("%s\n", s);
}

5-4.c

//strend(s, t)，如果字符串 t 出现在字符串 s 的尾部，该函数返回 1，否则返回 0

#include <stdio.h>

int strend(char*, char*);

int strend(char *s, char *t) {
    int l = 0;
    while(*s++);
    while(*t++)
        ++l;

    *--(--s);
    *--(--t);
    while(l--)
        if(*t-- != *s--)
            return 0;
    return 1;
}

int main(){
    char t[] = "0123456789abc";
    char s[] = "abc";
    printf("%d\n", strend(t, s));
}

5-9.c

#include <stdio.h>

static char daytab[2][13] = {
    {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
    {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};

int day_of_year(int year, int month, int day) {
    if(year <= 0 || month <= 0 || month > 12) return 0;
    int i, leap;
    leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
    for(i = 1; i < month; i++)
        day += *(*daytab + leap) + i;
    return day;
}


void month_day(int year, int yearday, int *pmonth, int *pday) {
    int i, leap;
    leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
    for(i = 1; yearday > daytab[leap][i]; i++)
        yearday -= *(*daytab + leap) + i;
    *pmonth = i;
    *pday = yearday;
}

int main(){
    printf("%d\n", day_of_year(2013, 1, 25));
    int a, b;
    month_day(2013, 50, &a, &b);
    printf("month = %d  day = %d\n", a, b);
    return 0;
}