---8.1---

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

int main(void)
{
    char *p;

    gets(p);
    printf("%s\n", p);
    return EXIT_SUCCESS;
}

修正部分
    char s[100];        /* �@ */
    p = s;              /* �A */

---8.2---

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

int main(void)
{
    char *p = "STRING";                               /* (1) */
    char s[] = "STRING";                              /* (2) */

    printf("#1: %c %c %c\n", *p, *p + 2, *(p + 4));   /* (3) */
    printf("#2: %c %c %c\n", p[0], p[0] + 2, p[4]);   /* (4) */
    p++;                                              /* (5) */
    printf("#3: %c %c %c\n", *p, *p + 2, *(p + 4));   /* (6) */
    printf("#4: %c %c %c\n", *s, *s + 2, *(s + 4));   /* (7) */
    printf("#5: %c %c %c\n", s[0], s[0] + 2, s[4]);   /* (8) */
    s++;                                              /* (9) */
    printf("#6: %c %c %c\n", *s, *s + 2, *(s + 4));   /* (10) */
    return EXIT_SUCCESS;
}

修正部分
    p = s + 1;                                        /* (9) */
    printf("#6: %c %c %c\n", *p, *p + 2, *(p + 4));   /* (10) */

---8.3---

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

void reverse(char s[]);

int main(void)
{
    char str[100];

    printf("文字列を入力して下さい：\n");
    gets(str);
    reverse(str);
    printf("逆転文字列：\n%s\n", str);
    return EXIT_SUCCESS;
}

void reverse(char *s)
{
    int w;
    char *p, *q;

    for (q = s; *q; q++)
        ;
    for (p = s; p < --q; p++) {
        w = *p; *p = *q; *q = w;
    }
}

---8.4---

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

void maxmin(int x[], int size, int *max, int *min);

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

    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();
    for (i = 0; i < n; i++) {
        printf("%6d", a[i]);
        if ((i + 1) % 10 == 0)
            printf("\n");
    }
    printf("\n");
    maxmin(a, n, &max, &min);
    printf("最大値は%d，最小値は%dです．\n", max, min);
    return EXIT_SUCCESS;
}

void maxmin(int x[], int size, int *max, int *min)
{
    int i, m, n;

    m = n = x[0];
    for (i = 1; i < size; i++) {
        if (x[i] > m)
            m = x[i];
        else if (x[i] < n)
            n = x[i];
    }
    *max = m;
    *min = n;
}

---8.5---

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

int main(int argc, char *argv[])
{
    int s, i;

    assert(argc > 1);
    s = 0;
    for (i = 1; i < argc; i++)
        s += atoi(argv[i]);
    printf("コマンド行引数の和は%dです．\n", s);
    return EXIT_SUCCESS;
}

---8.6---

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

struct item {
    struct item *next;
    int value;
};

int main(void)
{
    int n, i;
    struct item *root, *p, *q, *t;

    printf("データ数を入力して下さい：");
    scanf("%d", &n);
    assert(n > 0);
    root = NULL;
    for (i = 0; i < n; i++) {
        t = malloc(sizeof(struct item));      /* 要素の割り付け */
        t->value = rand();
        q = NULL; p = root;                   /* qとpの間に挿入する */
        while (p != NULL && t->value > p->value) {
            q = p; p = p->next;
        }
        t->next = p;
        if (q != NULL)
            q->next = t;
        else
            root = t;
    }
    for (p = root; p != NULL; p = p->next)    /* 全部の出力 */
        printf("%8d\n", p->value);
    return EXIT_SUCCESS;
}

---8.7---

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

double trapezoid(double (*func)(double), double a, double b, int n);
double sample(double x);

int main(void)
{
    printf("関数 4 / (1 + x * x) の区間[0, 1]における積分の近似値：\n");
    printf("%f\n", trapezoid(&sample, 0.0, 1.0, 10));
    return EXIT_SUCCESS;
}

double trapezoid(double (*func)(double), double a, double b, int n)
{
    double s, w;
    int i;

    s = (func(a) + func(b)) / 2.0;
    w = b - a;
    for (i = 1; i < n; i++)
        s += func(a + w * i / n);
    return s * w / n;
}

double sample(double x)
{
    return 4.0 / (1.0 + x * x);
}