=====第1章　練習問題=====

■1.1
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    printf("**************************\n");
    printf("*                        *\n");
    printf("* みなさん，こんにちは．   *\n");
    printf("*                        *\n");
    printf("**************************\n");
    return EXIT_SUCCESS;
}

■1.2
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    double a, b;

    scanf("%lf%lf", &a, &b);            /* 入力書式は %lf */
    printf("入力は %f と %f\n", a, b);  /* 出力書式は %f */
    printf("和は %f\n", a + b);
    printf("差は %f\n", a - b);
    printf("積は %f\n", a * b);
    printf("商は %f\n", a / b);
    return EXIT_SUCCESS;  /* 実数に対して % は定義されない */
}

■1.3
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int mile, yard;
    double km, ml;

    scanf("%lf", &km);
    mile = ml = km / 1.6093;  /* mile は ml の整数部分 */
    yard = (ml - mile) * 1760;
    printf("%.2fキロメートルは%dマイル%dヤードです．\n", km, mile, yard);
    return EXIT_SUCCESS;
}

■1.4
#include <stdio.h>
#include <stdlib.h>

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

    printf("2桁の整数を考えて下さい．\n");
    printf("それを7で割った余りはいくつですか？ ");
    scanf("%d", &a);
    printf("それを5で割った余りはいくつですか？ ");
    scanf("%d", &b);
    printf("それを3で割った余りはいくつですか？ ");
    scanf("%d", &c);
    printf("あなたが考えた数は %d です．\n",
        (15 * a + 21 * b + 70 * c) % 105);
    return EXIT_SUCCESS;
}

=====第2章　練習問題=====

■2.1
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int n, s;

    printf("入場者数を入力して下さい：");
    scanf("%d", &n);
    if (n < 20)
        s = 800 * n;
    else
        s = 750 * n;
    printf("入場料の合計は%d円です．\n", s);
    return EXIT_SUCCESS;
}

■2.2
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    double m;
    int f;

    printf("乗車距離（キロメートル）を入力して下さい：");
    scanf("%lf", &m);
    f = 650;
    if ((m -= 2.0) > 0.0)
        f += 80 * (int)((m + 0.5) / 0.6);
    printf("料金は%d円です．\n", f);
    return EXIT_SUCCESS;
}

■2.3
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int h, w, s;
    double f, stdw;

    printf("身長，体重，性別を入力して下さい：");
    scanf("%d%d%d", &h, &w, &s);
    if (s == 1)    /* 男 */
        stdw = (h - 139) * 0.613 + 42.2;
    else           /* 女 */
        stdw = (h - 139) * 0.510 + 43.2;
    f = (w - stdw) / stdw * 100;
    printf("あなたの肥満度は%.1fで，", f);
    if (f >= 20.0)
        printf("ふとりすぎです．\n");
    else if (f >= 10.0)                /* else が重要 */
        printf("ふとりぎみです．\n");
    else if (f > -10.0)
        printf("ふつうです．\n");
    else if (f > -20.0)
        printf("やせぎみです．\n");
    else
        printf("やせすぎです．\n");
    return EXIT_SUCCESS;
}

■2.4
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int m;

    printf("何月ですか？ ");
    scanf("%d", &m);
    printf("%d月は", m);
    switch (m) {
        case 1: case 3: case 5: case 7: case 8: case 10: case 12:
            printf("31日です．\n"); break;
        case 2:
            printf("28日です．\n"); break;
        case 4: case 6: case 9: case 11:
            printf("30日です．\n"); break;
        default:
            printf("ありません．\n");
    }
    return EXIT_SUCCESS;
}

=====第3章　練習問題=====

■3.1
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int main(void)
{
    int n, i;
    double s, f;

    printf("正整数を入力して下さい：");
    scanf("%d", &n);
    assert(n > 0);
    s = f = 1.0;
    for (i = 1; i <= n; i++)
        s += (f /= i);
    printf("和は%fです．\n", s);
    return EXIT_SUCCESS;
}

■3.2
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int i, j;

    printf("    ");                       /* 上の見出し */
    for (j = 0; j < 16; j++)
        printf("%4X", j);
    printf("\n");
    printf("    ");                       /* 境界線 */
    for (j = 0; j < 16; j++)
        printf("----");
    printf("\n");
    for (i = 0; i < 16; i++) {
        printf("%2X |", i);               /* 左の見出し */
        for (j = 0; j < 16; j++)
             printf("%4X", i + j);        /* 和 */
        printf("\n");
    }
    return EXIT_SUCCESS;
}

■3.3
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int n, i, c, maxc, maxn;

    maxc = 0;
    for (i = 1; i <= 100; i++) {
        n = i;
        c = 0;              /* 繰り返し回数 */
        while (n != 1) {
            if (n & 1)      /* 奇数 */
                n = 3 * n + 1;
            else            /* 偶数 */
                n >>= 1;
            c++;
        }
        if (c > maxc) {
            maxc = c; maxn = i;
        }
    }
    printf("%dの寿命が最も長く，%dです．\n", maxn, maxc);
    return EXIT_SUCCESS;
}

■3.4
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int a, b, c, a2, a2b2;

    for (a = 1; a < 99; a++) {
        a2 = a * a;
        for ( b = a + 1; b < 100; b++) {
            a2b2 = a2 + b * b;
            for (c = b + 1; c < 101; c++)
                if (c * c == a2b2)
                    printf("%4d%4d%4d\n", a, b, c);
        }
    }
    return EXIT_SUCCESS;
}

=====第4章　練習問題=====

■4.1
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int main(void)
{
    long pay;
    int m, d, c;

    printf("金額を入力して下さい：\n");
    scanf("%ld", &pay);
    assert(pay > 0);
    m = 10000; d = 2;
    while (pay) {
        c = pay / m;
        pay %= m;
        if (c)
            printf("%d円%d枚\n", m, c);
        m /= d;
        d = 10 / d;  /* d の値は，2, 5, 2, 5, … となる */
    }
    return EXIT_SUCCESS;
}

■4.2
#include <stdio.h>
#include <stdlib.h>

#define  MAX   1000
#define  NOB   8
#define  SIZE  (MAX / NOB + 1)

#define  POS(x)  (x / NOB)           /* 配列要素の位置 */
#define  MASK(x) (1 << (x % NOB))    /* マスク */

int main(void)
{
    char sieve[SIZE];
    int i, j, c;
/**/ /* 変更した行 */
    for (i = 0; i < SIZE; i++)        /* 2〜1000を書く */
/**/    sieve[i] = 0;
    for (i = 2; i * i <= MAX; i++) {
/**/    if ((sieve[POS(i)] & MASK(i)) == 0)   /* まだ残っている−−素数 */
            for (j = 2 * i; j <= MAX; j += i)
/**/            sieve[POS(j)] |= MASK(j);   /* 倍数を消す */
    }
    for (c = 0,i = 2; i <= MAX; i++)  /* 素数の出力 */
/**/    if ((sieve[POS(i)] & MASK(i)) == 0) {
            printf("%5d", i);
            if ((++c % 10) == 0)      /* 10個で改行 */
                printf("\n");
        }
    printf("\n");
    return EXIT_SUCCESS;
}

■4.3
#include <stdio.h>
#include <stdlib.h>

#define  M  20
#define  N  3

int main(void)
{
    int st[M + 1][N];
    int i, j, s;

    for (i = 0; i < M; i++)
        for (j = 0; j < N; j++)
            st[i][j] = rand() % 101;
    printf("      国語  数学  英語  合計\n");
    for (j = 0; j < N; j++)
        st[M][j] = 0;
    for (i = 0; i < M; i++) {
        printf("%2d: ", i + 1);
        s = 0;
        for (j = 0; j < N; j++) {
            printf("%6d", st[i][j]);
            s += st[i][j];
            st[M][j] += st[i][j];
        }
        printf("%6d\n", s);
    }
    printf("    ");
    for (j = 0; j < N; j++)
        printf("%6.1f", (double)st[M][j] / M);
    printf("\n");
    return EXIT_SUCCESS;
}

■4.4
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int main(void)
{
    int a[10], n, i, j;

    printf("1以上10以下の整数を入力して下さい：\n");
    scanf("%d", &n);
    assert(1 <= n && n <= 10);
    a[0] = 1;
    for (i = 0; i < n; i++) {
        a[i] = 1;
        for (j = i - 1; j > 0; j--)
            a[j] += a[j - 1];
        for (j = 0; j < n - i; j++)
            printf("  ");
        for (j = 0; j <= i; j++)
            printf("%4d", a[j]);
        printf("\n");
    }
    return EXIT_SUCCESS;
}

=====第5章　練習問題=====

■5.1
#include <stdio.h>
#include <stdlib.h>
#define SIZE  sizeof x / sizeof(int)

int search(int a[], int size, int key);

int main(void)
{
    int x[] = {30, 80, 70, 10, 60, 40, 90, 20, 50};

    if (search(x, SIZE, 60) >= 0)  printf("60はあります．\n");
    else                           printf("60はありません．\n");
    if (search(x, SIZE, 55) >= 0)  printf("55はあります．\n");
    else                           printf("55はありません．\n");
    return EXIT_SUCCESS;
}

int search(int a[], int size, int key)
{
    int i;

    for (i = 0; i < size && a[i] != key; i++)
        ;
    return i < size ? i : -1;
}

■5.2
#include <stdio.h>
#include <stdlib.h>
#define SIZE  sizeof x / sizeof(int)

int search(int a[], int size, int key);

int main(void)
{
    int x[] = {10, 20, 30, 40, 50, 60, 70, 80, 90};

    if (search(x, SIZE, 60) >= 0)  printf("60はあります．\n");
    else                        printf("60はありません．\n");
    if (search(x, SIZE, 55) >= 0)  printf("55はあります．\n");
    else                        printf("55はありません．\n");
    return EXIT_SUCCESS;
}

int search(int a[], int size, int key)
{
    int low, high, middle;

    low = 0; high = size - 1;
    while (low <= high) {
        middle = (low + high) / 2;
        if (a[middle] == key)
            return middle;
        if (a[middle] < key)
            low = middle + 1;
        else
            high = middle - 1;
    }
    return -1;
}

■5.3
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int gcd_a(int x, int y);    /* 再帰版 */
int gcd_b(int x, int y);    /* 非再帰版 */

int main(void)
{
    int x, y;

    printf("二つの整数を入力して下さい：");
    scanf("%d%d", &x, &y);
    assert(x >= 0 && y >= 0 && x + y != 0);
    printf("%dと%dの最大公約数は%dです．\n", x, y, gcd_a(x, y));
    printf("%dと%dの最大公約数は%dです．\n", x, y, gcd_b(x, y));
    return EXIT_SUCCESS;
}

/* どちらの方法も，x, y の大小関係は気にする必要がない */

int gcd_a(int x, int y)
{
    return x == 0 || y == 0 ? x + y : gcd_a(y, x % y);
}

int gcd_b(int x, int y)
{
    int w;

    while (x && y) {
        w = x % y;
        x = y;
        y = w;
    }
    return x + y;
}

■5.4
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int dgtl_rt(unsigned long n);

int main(void)
{
    unsigned long n;

    printf("負でない整数を入力して下さい：");
    scanf("%ld", &n);
    assert(n >= 0);
    printf("%ldのdigital rootは%dです．\n", n, dgtl_rt(n));
    return EXIT_SUCCESS;
}

int dgtl_rt(unsigned long n)
{
    return n < 10 ? (int)n : dgtl_rt(n / 10 + n % 10);
}

=====第6章　練習問題=====

■6.1
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    char str[100];
    int i, j, c;

    printf("文字列を入力して下さい：\n");
    gets(str);
    i = j = 0;
    do {
        c = str[i++];
        if (c != ' ')
            str[j++] = c;
    } while (c);
    printf("空白を削除した文字列は\n%s\nです．\n", str);
    return EXIT_SUCCESS;
}

■6.2
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int palin_E(char s[]);
int palin_J(char s[]);

int main(void)
{
    if (palin_E("madamimadam"))
        printf("madamimadam は回文です．\n");
    else
        printf("madamimadam は回文ではありません．\n");
    if (palin_J("たけやぶやけた"))
        printf("「たけやぶやけた」は回文です．\n");
    else
        printf("「たけやぶやけた」は回文ではありません．\n");
    if (palin_J("ねこのこのこねこ"))
        printf("「ねこのこのこねこ」は回文です．\n");
    else
        printf("「ねこのこのこねこ」は回文ではありません．\n");
    return EXIT_SUCCESS;
}

int palin_E(char s[])
{
    int i, j;

    i = 0;  j = strlen(s) - 1;
    while(i < j && s[i] == s[j]) {
        i++;  j--;
    }
    return i >= j;
}

int palin_J(char s[])
{
    int i, j;

    i = 0;  j = strlen(s) - 2;
    while(i < j && s[i] == s[j] && s[i + 1] == s[j + 1]) {
        i += 2;  j -= 2;
    }
    return i >= j;
}

■6.3
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <ctype.h>

void caesar(char s[], char t[], int cnt);

int main(void)
{
    char statement[100], cryptogram[100];
    int cnt;

    printf("文字列を入力して下さい：\n");
    gets(statement);
    printf("ずらし量を入力して下さい：\n");
    scanf("%d", &cnt);
    assert(0 < cnt && cnt < 26);
    caesar(statement, cryptogram, cnt);
    printf("暗号文：%s\n", cryptogram);
    return EXIT_SUCCESS;
}

void caesar(char s[], char t[], int cnt)
{
    int i, j, c;

    i = j = 0;
    do {
        c = s[i++];
        if (isalpha(c)) {
            c = tolower(c) + cnt;
            if (c > 'z')
                c -= 26;
            t[j++] = c;
        }
    } while (c);
    t[j] = '\0';
}

■6.4
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

void conv(char s[], unsigned long value, int base);

int main(void)
{
    char str[100];
    unsigned long value;
    int base;

    printf("整数を入力して下さい：\n");
    scanf("%lu", &value);
    printf("基底を入力して下さい：\n");
    scanf("%d", &base);
    assert(1 < base && base < 37);
    conv(str, value, base);
    printf("10進数%luは，%d進法で%sとなります．\n", value, base, str);
    return EXIT_SUCCESS;
}

void conv(char s[], unsigned long value, int base)
{
    static char digit[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    unsigned long v;
    int len;

    len = 0;  v = value;
    do {        /* 結果の長さを求める */
        len++;
        v /= base;
    } while (v);
    s[len] = '\0';
    v = value;
    do {
        s[--len] = digit[v % base];
        v /= base;
    } while (v);
}

=====第7章　練習問題=====

■7.1
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE  20

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

void gen_str(char s[], int n);
void display(struct student x[], int n);

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

    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);
    for (i = 0; i < SIZE; i++) {
        min = i;
        for (j = i + 1; j < SIZE; j++)
            if (strcmp(group[j].name, group[min].name) < 0)
                min = j;
        w = group[i]; group[i] = group[min]; group[min] = w;
    }
    printf("整列後：\n");
    display(group, SIZE);
    return EXIT_SUCCESS;
}

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

    for (i = 0; i < n; i++)
        printf("%-15s%4d\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';
}

■7.2
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE  20

struct student {
    char name[11];
    int point_a, point_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, j, max;

    for (i = 0; i < SIZE; i++) {
        gen_str(group[i].name, rand() % 5 + 6);
        group[i].point_a = rand() % 101;
        group[i].point_b = rand() % 101;
    }
    printf("整列前：\n");
    display(group, SIZE);
    for (i = 0; i < SIZE; i++) {
        max = i;
        for (j = i + 1; j < SIZE; j++)
            if (group[j].point_a > group[max].point_a
             || (group[j].point_a == group[max].point_a
              && group[j].point_b > group[max].point_b))
                max = j;
        w = group[i]; group[i] = group[max]; group[max] = w;
    }
    printf("整列後：\n");
    display(group, SIZE);
    return EXIT_SUCCESS;
}

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

    for (i = 0; i < n; i++)
        printf("%-15s%4d%4d\n", x[i].name, x[i].point_a, x[i].point_b);
}

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

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

■7.3
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

struct complex {
    double re, im;
};

struct complex cadd(struct complex a, struct complex b);
struct complex csub(struct complex a, struct complex b);
struct complex cmult(struct complex a, struct complex b);
struct complex cdiv(struct complex a, struct complex b);

/* a = 2 + i, b = 3 + 4i のとき，(a + b) / (a - b) を求める． */

int main(void)
{
    struct complex a = {2.0, 1.0}, b = {3.0, 4.0}, c;

    c = cdiv(cadd(a, b), csub(a, b));
    printf("(%f) + (%f)i\n", c.re, c.im);
    return EXIT_SUCCESS;
}

struct complex cadd(struct complex a, struct complex b)
{
    struct complex t;

    t.re = a.re + b.re;
    t.im = a.im + b.im;
    return t;
}

struct complex csub(struct complex a, struct complex b)
{
    struct complex t;

    t.re = a.re - b.re;
    t.im = a.im - b.im;
    return t;
}

struct complex cmult(struct complex a, struct complex b)
{
    struct complex t;

    t.re = a.re * b.re - a.im * b.im;
    t.im = a.re * b.im + a.im * b.re;
    return t;
}

struct complex cdiv(struct complex a, struct complex b)
{
    struct complex t;
    double denom;

    denom = b.re * b.re + b.im * b.im;
    assert(denom != 0.0);
    t.re = b.re;  t.im = -b.im;
    t = cmult(a, t);
    t.re /= denom;  t.im /= denom;
    return t;
}

■7.4
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

struct point {
    double x, y;
};

struct rect {
    struct point ul, lr;
};

int overlap(struct rect a, struct rect b);

int main(void)
{
    struct rect a = {{1.0, 4.0}, {3.0, 1.0}},
                b = {{2.0, 2.0}, {5.0, -1.0}},
                c = {{-5.0, 2.0}, {-1.0, -1.0}};

    if (overlap(a, b))  printf("a と b は重なります．\n");
    else                printf("a と b は重なりません．\n");
    if (overlap(a, c))  printf("a と c は重なります．\n");
    else                printf("a と c は重なりません．\n");
    return EXIT_SUCCESS;
}

int overlap(struct rect a, struct rect b)
{
    struct rect cover;

    assert(a.ul.x < a.lr.x && a.ul.y > a.lr.y);
    assert(b.ul.x < b.lr.x && b.ul.y > b.lr.y);
    cover.ul.x = a.ul.x < b.ul.x ? a.ul.x : b.ul.x;
    cover.ul.y = a.ul.y > b.ul.y ? a.ul.y : b.ul.y;
    cover.lr.x = a.lr.x > b.lr.x ? a.lr.x : b.lr.x;
    cover.lr.y = a.lr.y < b.lr.y ? a.lr.y : b.lr.y;
    return (a.lr.x - a.ul.x) + (b.lr.x - b.ul.x) > (cover.lr.x - cover.ul.x)
        && (a.ul.y - a.lr.y) + (b.ul.y - b.lr.y) > (cover.ul.y - cover.lr.y);
}

=====第8章　練習問題=====

■8.1
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE  20

struct student {
    char *name;
    int point;
};

void gen_str(char s[], int n);
void display(struct student x[], int n);

int main(void)
{
    struct student group[SIZE], w;
    int i, j, max;
    char nm[11];

    for (i = 0; i < SIZE; i++) {
        gen_str(nm, rand() % 5 + 6);
        group[i].name = malloc(strlen(nm) + 1);
        strcpy(group[i].name, nm);
        group[i].point = rand() % 101;
    }
    printf("整列前：\n");
    display(group, SIZE);
    for (i = 0; i < SIZE; i++) {
        max = i;
        for (j = i + 1; j < SIZE; j++)
            if (group[j].point > group[max].point)
                max = j;
        w = group[i]; group[i] = group[max]; group[max] = w;
    }
    printf("整列後：\n");
    display(group, SIZE);
    return EXIT_SUCCESS;
}

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

    for (i = 0; i < n; i++)
        printf("%-15s%4d\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';
}

■8.2
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *mystrstr(const char *s, const char *t);

int main(void)
{
    if (mystrstr("ABCDEFGHIJ", "EFG"))
        printf("ABCDEFGHIJ の中に EFG があります．\n");
    else
        printf("ABCDEFGHIJ の中に EFG はありません．\n");
    if (mystrstr("ABCDEFGHIJ", "EFX"))
        printf("ABCDEFGHIJ の中に EFX があります．\n");
    else
        printf("ABCDEFGHIJ の中に EFX はありません．\n");
    return EXIT_SUCCESS;
}

char *mystrstr(const char *s, const char *t)
{
    char *ss, *tt;

    while (*s) {
        ss = s;  tt = t;
        while (*tt && *ss == *tt) {
            ss++;  tt++;
        }
        if (*tt == '\0')
            return s;
        s++;
    }
    return NULL;
}

■8.3
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void insert(char *s, char *p, const char *t);
void reverse(char *s, char *t);

int main(void)
{
    char s[50], *p;

    strcpy(s, "ABCDEFG");
    p = strchr(s, 'D');
    insert(s, p, "XYZ");
    printf("ABCDEFG の D の前に XYZ を挿入すると %s となります．\n", s);
    return EXIT_SUCCESS;
}

void insert(char *s, char *p, const char *t)
{
    int ls, lt;

    ls = strlen(s);  lt = strlen(t);
    strcat(s, t);
    reverse(p, (s += ls) - 1);
    reverse(s, s + lt - 1);
    reverse(p, s + lt - 1);
}

void reverse(char *s, char *t)
{
    int c;

    while (s < t) {
        c = *s; *s++ = *t; *t-- = c;
    }
}

■8.4
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

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

void output(struct item *p);

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;
    }
    output(root);
    return EXIT_SUCCESS;
}

void output(struct item *p)
{
    if (p) {
        output(p->next);            /* �@ */
        printf("%8d\n", p->value);  /* �A */
    }                               /* �@，�Aを逆にすると昇順になょ?*/
}

=====第9章　練習問題=====

■9.1
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#define SIZE  100

int main(int argc, char *argv[])
{
    FILE *f;
    char buf[SIZE + 1];
    int lcnt;

    assert(argc == 3);
    f = fopen(argv[2], "r");
    if (f == NULL) {
        printf("ファイル%sがオープンできません．\n", argv[2]);
        return EXIT_FAILURE;
    }
    lcnt = 0;
    while (fgets(buf, SIZE, f)) {
        lcnt++;
        if (strstr(buf, argv[1]))
            printf("%6d: %s", lcnt, buf);
    }
    fclose(f);
    return EXIT_SUCCESS;
}

■9.2
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>

enum {false, true};

int main(int argc, char *argv[])
{
    FILE *f;
    int c, ccnt, lcnt, wcnt, wflag;

    assert(argc == 2);
    f = fopen(argv[1], "r");
    if (f == NULL) {
        printf("ファイル%sがオープンできません．\n", argv[1]);
        return EXIT_FAILURE;
    }
    ccnt = lcnt = wcnt = 0;  wflag = false;
    while ((c = fgetc(f)) != EOF) {
        ccnt++;
        if (isspace(c)) {
            wflag = false;
            if (c == '\n')
                lcnt++;
        }
        else if (!wflag) {
            wflag = true;
            wcnt++;
        }
    }
    fclose(f);
    printf("ファイル %s に含まれる\n", argv[1]);
    printf("    文字数は %d，行数は %d，単語数は %d\n", ccnt, lcnt, wcnt);
    printf("です．\n");
    return EXIT_SUCCESS;
}

■9.3
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>

void output(FILE *f, int c);

int main(int argc, char *argv[])
{
    FILE *inf, *outf;
    int c;

    assert(argc == 3);
    inf = fopen(argv[1], "rb");
    if (inf == NULL) {
        printf("ファイル%sがオープンできません．\n", argv[1]);
        return EXIT_FAILURE;
    }
    outf = fopen(argv[2], "w");
    if (outf == NULL) {
        printf("ファイル%sがオープンできません．\n", argv[2]);
        return EXIT_FAILURE;
    }
    do {
        c = fgetc(inf);
        output(outf, c);
    } while (c != EOF);
    fclose(inf);
    fclose(outf);
    return EXIT_SUCCESS;
}

void output(FILE *f, int c)
{
    static int shift = 2, cc = 0;
    static char ch[] = "0123456789abcdefghijklmnopqrstuvwxyz"
                       "ABCDEFGHIJKLMNOPQRSTUVWXYZ+-";

    cc <<= 8;
    if (c != EOF) {
        cc |= c;
        fputc(ch[(cc >> shift) & 0x3F], f);
        shift += 2;
        if (shift == 8) {
            fputc(ch[cc & 0x3F], f);
            shift = 2;
        }
    }
    else {
        if (shift != 2)
            fputc(ch[(cc >> shift) & 0x3F], f);
        fputc('*', f);
    }
}

■9.4
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>

void output(FILE *f, int c);

int main(int argc, char *argv[])
{
    FILE *inf, *outf;
    int c;

    assert(argc == 3);
    inf = fopen(argv[1], "r");
    if (inf == NULL) {
        printf("ファイル%sがオープンできません．\n", argv[1]);
        return EXIT_FAILURE;
    }
    outf = fopen(argv[2], "wb");
    if (outf == NULL) {
        printf("ファイル%sがオープンできません．\n", argv[2]);
        return EXIT_FAILURE;
    }
    while ((c = fgetc(inf)) != '*')
        output(outf, c);
    fclose(inf);
    fclose(outf);
    return EXIT_SUCCESS;
}

void output(FILE *f, int c)
{
    static int shift = 6, cc = 0;
    static char ch[] = "0123456789abcdefghijklmnopqrstuvwxyz"
                       "ABCDEFGHIJKLMNOPQRSTUVWXYZ+-";
    int i;

    for (i = 0; i < 64 && c != ch[i]; i++)
        ;
    if (i == 64) {
        printf("正しいファイルではありません．\n");
        exit(EXIT_FAILURE);
    }
    cc = (cc << 6) | i;
    if (shift < 6)
        fputc((cc >> shift) & 0xFF, f);
    shift -= 2;
    if (shift < 0)
        shift = 6;
}

=====第10章　練習問題=====

■10.1
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define PTFILE  "point.cnt"
#define MAX  5

struct record {
    long point;
    int year, month, day;
};

int main(void)
{
    struct record bests[MAX + 1], w;
    int cnt, i, k;
    FILE *f;
    time_t t;
    struct tm *pt;

    cnt = 0;
    f = fopen(PTFILE, "r");
    if (f) {
        while (fscanf(f, "%ld%d%d%d",
            &w.point, &w.year, &w.month, &w.day) == 4) {
            bests[0] = w;  /* 番兵 */
            for (k = cnt; w.point > bests[k].point; k--)
                ;
            if (k < MAX) {
                if (cnt < MAX)
                    cnt++;
                for (i = cnt - 1; i > k; i--)
                    bests[i + 1] = bests[i];
                bests[k + 1] = w;
            }
        }
        printf("現在までのベスト%d：\n", cnt);
        for (i = 1; i <= cnt; i++)
            printf("%2d: %ld 点（%d年%d月%d日)\n", i, bests[i].point,
                bests[i].year, bests[i].month, bests[i].day);
    }
    else
        printf("今回が最初です．\n");
    fclose(f);
    printf("\n今回の得点：");
    scanf("%ld", &w.point);
    time(&t);
    pt = localtime(&t);
    f = fopen(PTFILE, "a");
    if (f == NULL) {
        printf("ファイルがオープンできません．\n");
        exit(EXIT_FAILURE);
    }
    fprintf(f, "%ld %d %d %d\n", w.point,
        pt->tm_year + 1900, pt->tm_mon + 1, pt->tm_mday);
    fclose(f);
    return EXIT_SUCCESS;
}

■10.2
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>

char *concat(char *s, int n, ...);

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

    concat(s, 3, "abc", "12345", "+-*/");
    printf("%s\n", s);
    return EXIT_SUCCESS;
}

char *concat(char *s, int n, ...)
{
    va_list ap;

    va_start(ap, n);
    *s = '\0';
    while (n--) {
        strcat(s, va_arg(ap, char *));
    }
    va_end(ap);
    return s;
}

■10.3
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <assert.h>

long fib_a(int n);
long elapse(void);

enum {false, true};

int main(void)
{
    int n;
    long f;

    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)
    elapse();
    f = fib_a(n);
    printf("fib(%d) = %ldで，計算所要時間は%ld秒です．\n", n, f, elapse());
    return EXIT_SUCCESS;
}

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

long elapse(void)
{
    static int first = true;
    static time_t t0, t1;

    if (first)
        t1 = time(&t0);
    else
        time(&t1);
    first = !first;
    return (long)difftime(t1, t0);
}

■10.4
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define M  10
#define N  25

int mesh[M + 2][M + 2];

void island(int i, int j);

int main(void)
{
    int i, j, k, cnt;

    srand(time(NULL));
    for (i = 0; i < M + 2; i++)
        for (j = 0; j < M + 2; j++)
            mesh[i][j] = 0;
    k = 0;
    while (k < N) {
        i = rand() % M + 1;
        j = rand() % M + 1;
        if (!mesh[i][j]) {
            mesh[i][j] = 1;
            k++;
        }
    }
    cnt = 0;
    for (i = 1; i <= M; i++) {
        for (j = 1; j <= M; j++)
            printf("%s", mesh[i][j] == 0 ? "□" : "■");
        printf("\n");
    }
    for (i = 1; i <= M; i++)
        for (j = 1; j <= M; j++)
            if (mesh[i][j] > 0) {
                cnt++;
                island(i, j);
            }
    printf("\n島の個数は%dです．\n", cnt);
    return EXIT_SUCCESS;
}

void island(int i, int j)
{
    static int v[4] = {1, 0, -1, 0}, h[4] = {0, 1, 0, -1};
    int k, i1, j1;

    mesh[i][j] = -mesh[i][j];
    for (k = 0; k < 4; k++) {
        i1 = i + v[k];  j1 = j + h[k];
        if (mesh[i1][j1] > 0)
            island(i1, j1);
    }
}