• 程序清单12.1，hiding.c:

// hiding.c -- 块中的变量
#include <stdio.h>int main(void)
{int x = 30;            // 原始的 x printf("x in outer block: %d at %p\n", x, &x);{int x = 77;       // 新的 x, 隐藏了原始的 x printf("x in inner block: %d at %p\n", x, &x);}printf("x in outer block: %d at %p\n", x, &x);while (x++ < 33)      // 原始的 x {int x = 100;      // 新的 x, 隐藏了原始的 x x++;printf("x in while loop: %d at %p\n", x, &x);}printf("x in outer block: %d at %p\n", x, &x);return 0;
} 

输出结果：

• 程序清单12.2，forc99.c:

/* forc99.c -- 新的 C99 块规则 */
#include <stdio.h>int main(void)
{int n = 8;printf("    Initially, n = %d at %p\n", n, &n);for (int n = 1; n < 3; n++)printf("      loop 1: n = %d at %p\n", n, &n);printf("After loop 1, n = %d at %p\n", n, &n);for (int n = 1; n < 3; n++){printf("  loop 2 index n = %d at %p\n", n, &n);int n = 6;printf("  loop 2: n = %d at %p\n", n, &n);n++;}printf("After loop 2, n = %d at %p\n", n, &n);return 0;
}

输出结果：

• 程序清单12.3，loc_stat.c:

/* loc_stat.c -- 使用局部静态变量 */
#include <stdio.h>void trystat(void);int main(void)
{int count;for (count = 1; count <= 3; count++){printf("Here comes iteration %d:\n", count);trystat();}return 0;
}void trystat(void)
{int fade = 1;static int stay = 1;printf("fade = %d and stay = %d\n", fade++, stay++);
}

输出结果：

• 程序清单12.4，global.c:

/* global.c -- 使用外部变量 */
#include <stdio.h>int units = 0; /* 外部变量 */
void critic(void);int main(void)
{extern int units; /* 可选的重复声明 */ printf("How many pounds to a firkin of butter?\n");scanf("%d", &units);while (units != 56)critic();printf("You must looked it up!\n") ;return 0;
}void critic(void)
{/* 删除了可选的重复声明 */ printf("No luck, my friend. Try again.\n");scanf("%d", &units);
}

输出结果：

• 程序清单12.5，12.6，该项目由两个源文件组成。

parta.c:

// parta.c -- 不同的存储类别
// 与partb.c 一起编译
#include <stdio.h>void report_count();
void accumulate(int k);
int count = 0; //文件作用域，外部链接int main(void)
{int value; //自动变量register int i; //寄存器变量printf("Enter a positive integer (0 to quit): ");while (scanf("%d", &value) == 1 && value > 0){++count; //使用文件作用域变量for (i = value; i >= 0; i--)accumulate(i);printf("Enter a positive integer (0 to quir): ");}report_count();return 0;
}void report_count()
{printf("Loop executed %d times\n", count);
}

partb.c:

// partb.c -- 程序的其余部分
// 与 parta.c 一起编译
#include <stdio.h>extern int count; //引用式声明，外部链接static int total = 0; //静态定义，内部链接
//void accumulate(int k);void accumulate(int k) //k具有块作用域，无链接
{static int subtotal = 0; //静态，无链接if (k <= 0){printf("loop cycle: %d\n", count);printf("subtotal :%d; total: %d\n", subtotal, total);subtotal = 0;}else{subtotal += k;total += k;}
}

输出结果：

• 程序清单12.7，12.8，该项目包括两个源文件。

rand0.c:

/* rand0.c -- 生成随机数 */
/* 使用 ANSI C 可移植算法 */
static unsigned long int next = 1; /* 种子 */ unsigned int rand0(void)
{/* 生成伪随机数的魔术公式 */ next = next * 1103515245 + 12345;return (unsigned int) (next / 65536) % 32768;
}

r_drive0.c:

/* r_drive0.c -- 测试 rand0() 函数 */
/* 与 rand0.c 一起编译 */
#include <stdio.h>
extern unsigned int rand0(void); //extern可省略 int main(void)
{int count;for (count = 0; count < 5; count++)printf("%d\n", rand0());return 0;
}

输出结果：

• 程序清单12.9，12.10，该项目包含两个源文件。

s_and_r.c:

/* s_and_r.c -- 包含rand1() 和 srand1() 的文件 */
/* 使用 ANSI C 可移植算法 */
static unsigned long int next = 1; /* 种子 */ int rand1(void)
{/* 生成伪随机数的魔术公式 */ next = next * 1103515245 + 12345;return (unsigned int) (next / 65536) % 32768;
}void srand1(unsigned int seed)
{next = seed;
}

r_drive1.c:

/* r_drive1.c -- 测试rand1() 和 srand1() */
/* 与 s_and_r.c 一起编译 */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>extern void srand1(unsigned int x); // extern 可选
extern int rand1(void);int main(void)
{int count;//unsigned seed;int num = 1;time_t *a = 0;//printf("Please enter your choice for seed.\n");while (num-- > 0){srand1((unsigned int) time(a));for (count = 0; count < 5; count++)printf("%d\n", rand1());//printf("Please enter next seed (q to quit):\n");}printf("Done\n");return 0;
} 

输出结果：

• 程序清单12.11，12.12，12.13，该项目包含了一个头文件和两个源文件。

diceroll.h:

// diceroll.h
extern int roll_count;int roll_n_dice(int dice, int sides);

diceroll.c:

/* diceroll.c -- 掷骰子模拟程序 */
/* 与 manydice.c 一起编译 */
#include "diceroll.h"
#include <stdio.h>
#include <stdlib.h>          /* 提供库函数 rand() 的原型 */ int roll_count = 0;          /* 外部链接 */ static int rollem(int sides) /* 该函数属于该文件私有 */
{int roll;roll = rand() % sides + 1;++roll_count;            /* 计算函数调用次数 */ return roll;
}int roll_n_dice(int dice, int sides)
{int d;int total = 0;if (sides < 2){puts("Need at least 2 sides.");return -1;}if (dice < 1){puts("Need at least 1 dice.");return -1;}for (d = 0; d < dice; d++)total += rollem(sides);return total;
}

manydice.c:

/* manydice.c -- 多次掷骰子的模拟程序 */
/* 与 diceroll.c 一起编译 */
#include <stdio.h>
#include <stdlib.h>     /* 为库函数 srand() 提供原型 */
#include <time.h>       /* 为 time() 提供原型 */
#include "diceroll.h"   /* 为 roll_n_dice() 提供原型，为 roll_count 变量提供声明 */ int main(void)
{int dice, roll;int sides;int status;srand((unsigned int) time(0)); //重置种子 printf("Enter the number of sides per dice, 0 to stop.\n");while (scanf("%d", &sides) == 1 && sides > 0){printf("How many dice?\n");if ((status = scanf("%d", &dice)) != 1){if (status == EOF)break;           // 退出循环 else{printf("You should have enterd an integer.");printf("Let's begin again.\n");while (getchar() != '\n')continue;    // 处理错误的输入 printf("How many sides? Enter 0 to stop.\n");continue;        // 进入循环的下一轮迭代 */ }}roll = roll_n_dice(dice, sides);printf("You have rolled a %d using %d %d-sided dice.\n",roll, dice, sides);printf("How many sides? Enter 0 to stop.\n");}printf("The rollem() function was called %d times.\n",roll_count);             // 使用外部变量 printf("GOOD FORTUNE TO YOU!\n");return 0;
}

输出结果：

• 编程练习

题目1，方法：使用指针传递参数。示例代码12_1.c:

#include <stdio.h>void critic(int *);int main(void)
{int units;printf("How many pounds to a firkin of butter?\n");scanf("%d", &units);while (units != 56)critic(&units);printf("You must looked it up!\n") ;return 0;
}void critic(int * num)
{printf("No luck, my friend. Try again.\n");scanf("%d", num);
}

输出结果：

题目2，方法：根据选择以不同模式计算油耗。该项目由一个头文件和两个源文件组成。

pe12_2a.h:

void set_mode(int);
void get_info(void);
void show_info(void);

pe12_2a.c:

#include <stdio.h>
#include "pe12_2a.h"static int mode; // 静态变量自动初始化为 0
static double distance;
static double fuel;void set_mode(int num)
{if (num > 1){printf("Invalid mode specified. Mode %s used.\n",(0 == mode) ? "0(metric)" : "1(US)");}    elsemode = num; // 改变了具有文件作用域的静态变量 mode, 在程序执行期间不改变
}void get_info(void)
{if (0 == mode)printf("Enter distance traveled in kilometers: ");elseprintf("Enter distance traveled in miles: ");scanf("%lf", &distance);if (0 == mode)printf("Enter fuel consumed in liters: ");elseprintf("Enter fuel consumed in gallons: ");scanf("%lf", &fuel);
}void show_info(void)
{if (0 == mode)printf("Fuel consumption is %.1lf liters per 100 km.\n", (fuel / distance) * 100);elseprintf("Fuel consumption is %.1lf miles per gallon.\n", distance / fuel);
}

pe12_2b.c:

#include <stdio.h>
#include "pe12_2a.h"int main(void)
{int mode;printf("Enter 0 for metric mode, 1 for US mode: ");scanf("%d", &mode);while (mode >= 0){set_mode(mode);get_info();show_info();printf("Enter 0 for metric mode, 1 for US mode");printf(" (-1 to to quit): ");scanf("%d", &mode);}printf("Done.\n");return 0;
}

输出结果：

题目3，方法：使用自动变量改写题目2。该项目包含一个头文件和两个源文件。

pe12_3a.h:

void set_mode(int *);
void get_info(int, double *, double *);
void show_info(int, double, double);

pe12_3a.c:

#include <stdio.h>
#include "pe12_3a.h"void set_mode(int * n1)
{if (*n1 > 1){*n1 = 0;printf("Invalid mode specified. Mode %s used.\n", (0 == *n1) ? "0(metric)" : "1(US)");}
}void get_info(int n, double * n1, double * n2)
{if (0 == n)printf("Enter distance traveled in kilometers: ");elseprintf("Enter distance traveled in miles: ");scanf("%lf", n1);if (0 == n)printf("Enter fuel consumed in liters: ");elseprintf("Enter fuel consumed in gallons: ");scanf("%lf", n2);
}void show_info(int n, double n1, double n2)
{if (0 == n)printf("Fuel consumption is %.1lf liters per 100 km.\n", (n2 / n1) * 100);elseprintf("Fuel consumption is %.1lf miles per gallon.\n", n1 / n2);
}

pe12_3b.c:

#include <stdio.h>
#include "pe12_3a.h"int main(void)
{int mode;double distance, fuel;printf("Enter 0 for metric mode, 1 for US mode: ");scanf("%d", &mode);while (mode >= 0){set_mode(&mode);get_info(mode, &distance, &fuel);show_info(mode, distance, fuel);printf("Enter 0 for metric mode, 1 for US mode");printf(" (-1 to to quit): ");scanf("%d", &mode);}printf("Done.\n");return 0;
}

输出结果：

题目4，方法：测试函数被调用次数。示例代码：

#include <stdio.h>int call_times(void);int main(void)
{int i, num;for (i = 0; i < 10; i++)num = call_times();printf("I have been called %d times.\n", num);return 0;
}int call_times(void)
{static int count = 0;count++;return count;
}

输出结果：

题目5，方法：生成随机数并排序。示例代码12_5.c:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define LEN 10void sort_array(int, int *);
void show_array(int, const int *);int main(void)
{int i;int * ar;ar = (int *) malloc(LEN * sizeof(int));srand((unsigned int) time(0));for (i = 0; i < LEN; i++)*(ar + i) = (rand() % 10) + 1; // 生成 1~10 的随机数 printf("Before sorted:\n");show_array(LEN, ar);sort_array(LEN, ar);printf("\n\nAfter sorted:\n");show_array(LEN, ar);free(ar);return 0;}void sort_array(int n, int * ar) // 冒泡排序
{int i, j, temp;for (i = 0; i < n - 1; i++)for (j = i + 1; j < n; j++)if (*(ar +i) < *(ar + j)){temp = *(ar + i);*(ar + i) = *(ar + j);*(ar + j) = temp;}
}void show_array(int n, const int * ar)
{int i;for (i = 0; i < n; i++){printf("%-3d", *(ar + i));if ((i + 1) % 5 == 0)putchar('\n');}
}

输出结果（以10个数测试）：

题目6，方法：测试不同随机数种子生成的不同数字出现的次数。示例代码12_6.c:

#include <stdio.h>
#include <stdlib.h>
#define LEN 10
#define MAX 1000int main(void)
{int i, j;int ar[LEN];unsigned int seed;for (i = 0; i < LEN; i++, seed = i){printf("\n%dth time,seed: %u\n\n", i + 1, seed);srand(seed);for (j = 0; j < LEN; j++) // 初始化保存出现次数的数组 *(ar + j) = 0;for (j = 0; j < MAX; j++) // 记录 0~9 出现的次数，类似 1~10 ar[(rand() % 10)]++;for (j = 0; j < LEN; j++)printf("%d appeared %d times.\n", j + 1, ar[j]);}return 0;
}

输出结果：

题目7，方法：掷骰子修改。示例代码12_7.c:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>int rollem(int n); //生成随机数 int main(void)
{int sets; //摇多少次骰子int count; //计数每次的点数int sides; //骰子的面数int dices; //每次几个骰子int i, j; //用于循环 printf("Enter the number of sets; enter q to stop: ");srand((unsigned int) time(0));while (scanf("%d", &sets) == 1 || sets < 1){printf("How many sides and how many dice? ");while (scanf("%d%d", &sides, &dices) != 2 || sides < 2 || dices < 1){printf("Input illegal, try again: ");while (getchar() != '\n')continue;}for (i= 0; i < sets; i++){count = 0; //每次摇动骰子之前初始化;for (j = 0; j < dices; j++)count += rollem(sides);printf("%dth time, total count: %d\n", i + 1, count); }printf("How many sets? Enter q to stop: ");}return 0;
}int rollem(int n)
{return rand() % n + 1;
}

输出结果：

题目8，方法：使用 malloc() 代替数组。示例代码12_8.c:

#include <stdio.h>
#include <stdlib.h>int * make_array(int elem, int val);
void show_array(const int ar[], int n);int main(void)
{int * pa;int size;int value;printf("Enter the number of elements: ");while (scanf("%d", &size) == 1 && size > 0){printf("Enter the initialization value: ");scanf("%d", &value);pa = make_array(size, value);if (pa){show_array(pa, size);free(pa);}printf("\nEnter the number of elements (<1 to quit): ");}printf("Done.\n");return 0;
}int * make_array(int elem, int val)
{int * index;int i;index = (int *) malloc(elem * sizeof(int));if (NULL == index)exit(EXIT_FAILURE);for (i = 0; i < elem; i++)*(index + i) = val;return index;
}void show_array(const int ar[], int n)
{int i;for (i = 0; i < n; i++){printf("%-3d", *(ar + i));if ((i + 1) % 8 == 0)putchar('\n');}
}

输出结果：

题目9，方法：保存单词并打印。示例代码12_9.c:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LEN 256int main(void)
{int words; //单词数量int size; //单词大小char ** pt; //保存单词的地址（指针的指针） char temp[LEN]; //临时保存单词 int i;printf("How many words do you wish to enter? ") ;scanf("%d", &words);if ((pt = (char **) malloc(words * sizeof(char *))) != NULL){printf("Enter %d words now:\n", words);for (i = 0; i < words; i++){scanf("%s", temp);size = strlen(temp) + 1; //多 1 个字节存储空字符 *(pt + i) = (char *) malloc(size * sizeof(char));if (*(pt + i) == NULL)exit(EXIT_FAILURE);strcpy(*(pt + i), temp); //将字符串从临时数组拷贝到malloc分配的空间 }printf("Here are your words:\n") ;for (i = 0; i < words; i++){puts(*(pt + i));free(*(pt + i));*(pt + i) = NULL;}free(pt);pt = NULL;}elseexit(EXIT_FAILURE);return 0;
}

输出结果：