#5-6,7 포인터 배열

[예제 5-7]

readlines 프로그램을 고쳐서 alloc 함수를 사용하지 않고 main에서 사용 가능한 배열에 입력을 저장하도록 해보라.

프로그램 수행이 얼마나 빨라지는지 보라. (시간 함수를 아직 잘 못쓰겠다.) . --> 해결! : 터미널에 time ./main 하면 실행 시간을 알 수 있다.

/* Reverse polish calculator */
/
#include <stdio.h>
#include <stdlib.h>        /* for atof() */
#include <math.h>        /* for fmod() */
 
#define MAXOP 100        /* max size of operand or operator */
#define NUMBER '0'        /* signal that a number was found */
 
int getop(char[]);
void push(double);
double pop(void);
void clear(void);
int getline(char*, int);
 
/* reverse Polish calculator */
// main.c
main() {
    int type;
    double op1, 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 '%': // 실수일 경우 정수로 만들어서 % 연산함
            op2 = pop();
            if (op2 != 0)
                push(fmod(pop(), op2));
            else
                printf("error: zero divisor\n");
            break;
        case 't':    /* show top element of stack */
            op2 = pop();
            printf("\t%.8g\n",op2);
            push(op2);
            break;
        case 'c':    /* clear the stack */
            clear();
            break;
        case 'd':    /* duplicate top element */
            op2 = pop();
            push(op2);
            push(op2);
            break;
        case 's':    /* swap the top two element */
            op1 = pop();
            op2 = pop();
            push(op1);
            push(op2);
            break;
        case '\n':
            printf("\t%.8g\n", pop());
            break;
        default:
            printf("error: unknow command %s\n", s);
            break;
        }
    }
}
 
// stack.c
#define MAXVAL 100        /* maximum depth of val stack */
int sp = 0;                /* next free stack position */ 
double val[MAXVAL];        /* val 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;
    }
}
 
/* clear:  clear the stack */
void clear(void)
{
    sp = 0;
}
 
// getop.c
#include <ctype.h>
 
int getch(void);
void ungetch(int);
 
#include <string.h>
#include <time.h>
 
#define MAXLINES 5000
char *lineptr[MAXLINES];
char linestor[MAXLINES];
 
void swap(char *v[], int i, int j);
void qsort(char *v[], int left, int right);
int readlines(char*lineptr[], char *linestor, int nlines);
void writelines(char *lineptr[], int nlines);
 
main()
{
    int nlines;        /* number of input lines read */
 
    if ((nlines = readlines(lineptr, linestor, MAXLINES)) >= 0)
    {
        qsort(lineptr, 0, nlines - 1);
        writelines(lineptr, nlines); 
        return 0;
    }
    else
    {
        printf("error: input too big to sort\n");
        return 1;
    }
 
}
 
#define MAXLEN 1000        /* max length of any input line */
#define MAXSTOR 5000
 
int mgetline(char *, int);
 
int readlines(char *lineptr[], char *linestor, int maxlines)
{
    int len, nlines;
    char line[MAXLEN];
    char *p = linestor;
    char *linestop = linestor + MAXSTOR;
 
    nlines = 0;
 
    while ((len = mgetline(line, MAXLEN)) > 0)
        if (nlines >= maxlines || p + len > linestop)
            return -1;
        else
        {
            line[len - 1] = '\0'; /* delete newlines */
            strcpy(p, line);
            lineptr[nlines++] = p;
            p += len;
        }
    return nlines;
}
 
int mgetline(char *s, int lim)
{
    int c;
    char *t = s;
 
    while (--lim > 0 && (c = getchar()) != EOF && c != '\n')
        *s++ = c;
    if (c == '\n')
        *s++ = c;
 
    *s = '\0';
 
    return s - t;
}
/* qsort: sort v[left] ... v[right] into increasing order */
void qsort(char *v[], int left, int right)
{
    int i, last;
    void swap(char *v[], int i, int j);
 
    if (left >= right)
        return;
    swap(v, left, (left + right) / 2);
 
    last = left;
 
    for (i = left + 1; i <= right; i++)
        if (strcmp(v[i], v[left])<0)
            swap(v, ++last, i);
    swap(v, left, last);
    qsort(v, left, last - 1);
    qsort(v, last + 1, right);
}
 
void writelines(char *lineptr[], int nlines) {
    int i;
    
    for (i = 0; i < nlines; i++)
        printf("%s\n", lineptr[i]);
}
/* swap: interchange v[i] and v[j] */
void swap(char *v[], int i, int j)
{
    char *temp;
 
    temp = v[i];
    v[i] = v[j];
    v[j] = temp;
}

[예졔 5-8]

day_of_year와 month_day 함수에 에러 검사하는 부분을 첨가해보라.

#include <stdio.h>
 
int day_of_year(int, int, int);
void month_day(int yeat, int yearday);
 
main()
{
    int day;
    int pmon[] = { 0 };
    int pday[] = { 0 };
 
    day = day_of_year(1988, 2, 29);
    printf("%d\n", day);
    month_day(1988, 60, pmon, pday);
    printf("mon: %d\tday: %d\n", *pmon, *pday);
    return;
}
/* day_of_year: set day of year from month & day */
int day_of_year(int year, int month, int day)
{
    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;
}
 
/* month_day: set month, day from day of year */
void month_day(int year, int yearday, int *pmonth, int *pday) {
    int i, leap;
    //check leap year
    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;
}

[예제 5- 9]

day_of_year와 month_day 함수를 포인터를 사용하도록 고쳐라.

#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, int, int);
void month_day(int yeat, int yearday);
 
main()
{
    int day;
    int pmon[] = { 0 };
    int pday[] = { 0 };
 
    day = day_of_year(1988, 2, 29);
    printf("%d\n", day);
    month_day(1988, 60, pmon, pday);
    printf("mon: %d\tday: %d\n", *pmon, *pday);
    return;
}
/* day_of_year: set day of year from month & day */
int day_of_year(int year, int month, int day)
{
    int i, leap;
    char *p;
    
    leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
 
    p = &daytab[leap][1]; // 처음에 1월을 가리키도록 초기화
 
    for (i = 1; i < month; i++)
        day += *p++;
 
    return day;
}
 
/* month_day: set month, day from day of year */
void month_day(int year, int yearday, int *pmonth, int *pday) {
    int i, leap;
    char *p;
    //check leap year
    leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
 
    p = &daytab[leap][1];
    for (i = 1; yearday > daytab[leap][i]; i++)
        yearday -= *p++;
 
    *pmonth = i;
    *pday = yearday;
}