---10.1---

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

int main(void)
{
    char card[52];
    char *suit[] = {"C", "D", "H", "S"};
    char *pip[] = {"A", "2", "3", "4", "5", "6", "7",
                   "8", "9", "10", "J", "Q", "K"};
    int i, k, w;

    for (i = 0; i < 52; i++)
        card[i] = i;
    for (i = 51; i > 0; i--) {
        k = rand() % i;
        w = card[i]; card[i] = card[k]; card[k] = w;
    }
    for (i = 0; i < 52; i++) {
        printf("%s%s ", suit[card[i] / 13], pip[card[i] % 13]);
        if ((i + 1) % 13 == 0)
            printf("\n");
    }
    return EXIT_SUCCESS;
}

---10.2---

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

long fib_a(int n);

int main(void)
{
    int n;
    long f;
    time_t t0, t1;

    printf("0以上45以下の整数を入力して下さい：");
    scanf("%d", &n);
    assert(0 <= n && n <=45)
    time(&t0);
    f = fib_a(n);
    time(&t1);
    printf("fib(%d) = %ldで，所要計算時間は%.0f秒です．\n",
        n, f, difftime(t1, t0));
    return EXIT_SUCCESS;
}

long fib_a(int n)
{
    return n < 2 ? 1 : fib_a(n - 1) + fib_a(n - 2);
}

---10.3---

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

int isleap(int year);

int main(void)
{
    static char days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int i, y, m, d, wd;
    time_t t;
    struct tm *tp;

    time(&t);
    tp = localtime(&t);
    y = 1900 + tp->tm_year;
    m = tp->tm_mon;
    d = days[m];
    wd = tp->tm_wday - (tp->tm_mday - 1) % 7;  /* 当月の1日の曜日 */
    if (wd < 0)
        wd += 7;
    if (m == 1 && isleap(y))
        d++;
    printf("%14d年%2d月\n", y, m + 1);
    printf("　日　月　火　水　木　金　土\n");
    for (i = 0; i < wd; i++)
        printf("    ");
    for (i = 1; i <= d; i++) {
        printf("%4d", i);
        if ((i + wd) % 7 == 0)
            printf("\n");
    }
    printf("\n");
    return EXIT_SUCCESS;
}

int isleap(int year)
{
    return (year % 400) || ((year % 100) && (year % 4 == 0));
}

---10.4---

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

#define SIZE  20

struct student {
    char name[11];
    int point;
};

int comp(const void *a, const void *b);
void gen_str(char s[], int n);
void display(struct student x[], int n);

int main(void)
{
    struct student group[SIZE], w;
    int i;

    for (i = 0; i < SIZE; i++) {
        gen_str(group[i].name, rand() % 5 + 6);
        group[i].point = rand() % 101;
    }
    printf("整列前：\n");  display(group, SIZE);
    qsort(group, SIZE, sizeof(struct student), &comp);
    printf("整列後：\n");  display(group, SIZE);
    return EXIT_SUCCESS;
}

int comp(const void *a, const void *b)
{          /* キャストとa, bの順序に注意 */
    return ((struct student *)b)->point - ((struct student *)a)->point;
}

void display(struct student x[], int n)
{
    int i;

    for (i = 0; i < n; i++)
        printf("%-15s%3d\n", x[i].name, x[i].point);
}

void gen_str(char s[], int n)
{
    int i;

    for (i = 0; i < n; i++)
        s[i] = rand() % 26 + 'a';
    s[i] = '\0';
}

---10.5---

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

void sort(int x[], int size);
void display(int x[], int size);
int comp(const void *a, const void *b);
int ascend(void *base, size_t n, size_t size,
        int (*comp)(const void *, const void *));

int main()
{
    int a[100];
    int n, i;

    printf("1以上100以下の整数を入力して下さい：");
    scanf("%d", &n);
    assert(1 <= n && n <= 100);
    for (i = 0; i < n; i++)
        a[i] = rand();
    printf("整列前：\n");
    display(a, n);
    if (ascend(a, n, sizeof(int), comp))
        printf("整列しています．\n");
    else
        printf("整列していません．\n");
    sort(a, n);
    printf("\n整列後：\n");
    display(a, n);
    if (ascend(a, n, sizeof(int), comp))
        printf("整列しています．\n");
    else
        printf("整列していません．\n");
    return EXIT_SUCCESS;
}

int ascend(void *base, size_t n, size_t size,
        int (*comp)(const void *, const void *))
{
    int i;
    char *p;

    for (p = base, i = 1; i < n && comp(p, p + size) <= 0; i++, p += size)
        ;
    return i == n;
}

int comp(const void *a, const void *b)
{
    return *(int *)a - *(int *)b;
}

void sort(int x[], int size)
{
    int i, j, min, w;

    for (i = 0; i < size; i++) {
        min = i;
        for (j = i + 1; j < size; j++)
            if (x[j] < x[min])
                min = j;
            w = x[i]; x[i] = x[min]; x[min] = w;
    }
}

void display(int x[], int size)
{
    int i;

    for (i = 0; i < size; i++) {
        printf("%6d", x[i]);
        if ((i + 1) % 10 == 0)
            printf("\n");
    }
    if (size % 10)
        printf("\n");
}

---10.6---

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

int maxval(int n, ...);

int main(void)
{
    int a[4];
    int i, j;

    for (i = 0; i < 4; i++) {
        a[i] = rand();
        printf("%d ", a[i]);
    }
    printf("\n");
    printf("三つの中の最大値：%d\n", maxval(3, a[0], a[1], a[2]));
    printf("四つの中の最大値：%d\n", maxval(4, a[0], a[1], a[2], a[3]));
    return EXIT_SUCCESS;
}

int maxval(int n, ...)
{
    va_list ap;
    int m, t;

    assert(n > 0);
    va_start(ap, n);
    m = va_arg(ap, int);
    while(--n) {
        t = va_arg(ap, int);
        if (t > m)
            m = t;
    }
    va_end(ap);
    return m;
}

---10.7---

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <assert.h>

double maxval(char *s, ...);

int main(void)
{
    printf("二つの中の最大値：%f\n", maxval("ii", 5, 3));
    printf("三つの中の最大値：%f\n", maxval("ldi", 5L, 7.0, 3));
    return EXIT_SUCCESS;
}

double maxval(char *s, ...)
{
    va_list ap;
    double m, t;
    char *p;

    assert(*s);
    p = s;
    va_start(ap, n);
    while (*p) {
        switch (*p) {
            case 'i': t = va_arg(ap, int); break;
            case 'l': t = va_arg(ap, long); break;
            case 'd': t = va_arg(ap, double); break;
            default: exit(EXIT_FAILURE);
        }
        if (p == s || t > m)
            m = t;
        p++;
    }
    va_end(ap);
    return m;
}

---10.8---

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

#define new_assert(e, m) \
    if (!(e)) {\
        fprintf(stderr, "表明" #e "が成り立ちません．\n");\
        fprintf(stderr, #m "\n");\
        abort();\
    }

int main(void)
{
    double a, b, c, s;

    printf("三つの実数を入力して下さい：");
    scanf("%lf%lf%lf", &a, &b, &c);
    new_assert(a + b > c && c > fabs(a - b), 三角形になりません．);
    s = (a + b + c) / 2.0;
    printf("三角形の面積は%.2fです．\n",
        sqrt(s * (s - a) * (s - b) * (s - c)));
    return EXIT_SUCCESS;
}