C Primer Plus 第12章_存储类别、链接和内存管理_代码和练习题

随机数函数和静态变量

/* r_drive0.c---测试rand0()函数 */
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
extern unsigned int rand0(void);

int main(void)
{
    
	int count;

	for (count = 0; count < 5; count++) {
    
		printf("%d\n", rand0());
	}

	return 0;
}

/* rand0.c --生成随机数*/
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_drive1.c */
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
extern int rand1(void);
extern void srand1(unsigned int x);

int main(void)
{
    
	int count;
	unsigned seed;

	printf("Please enter your choice for seed.\n");
	while (scanf("%u", &seed) == 1) {
    
		srand1(seed);
		for (count = 0; count < 5; count++) {
    
			printf("%d\n", rand1());
		}
		printf("Please enter next seed （q to quit):\n");
	}

	printf("Done\n");

	return 0;
}

/* s_and_r.c */
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;
}

掷骰子

/* diceroll.c--掷骰子模拟程序*/
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <time.h>
#include "diceroll.h"

int roll_count = 0;

static int rollem(int sides)
{
    
	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) {
    
		printf("Need at least 2 sides.\n");
		return -2;
	}
	if (dice < 1) {
    
		printf("Need at least 1 die.\n");
		return -1;
	}

	for (d = 0; d < dice; d++) {
    
		total += rollem(sides);
	}

	return total;
}

/* diceroll.h */
#pragma once
extern int roll_count;

int roll_n_dice(int dice, int sides);

/* manydice.c--一起编译 */
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <time.h>
#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));							/* 随机种子 */
	printf("Enter the number of sides per die, 0 to stop.\n");
	while (scanf("%d", &sides) == 1 && sides > 0) {
    
		printf("How many dices?\n");
		if (status = scanf("%d", &dice) != 1) {
    
			if (status == EOF) {
    
				break;										/* 退出循环 */
			}
			else {
    
				printf("You should have entered 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;									/* 进入循环的下一次迭代 */
 			}
		}
		roll = roll_n_dice(dice, sides);
		printf("You have rolled a %d using %d %d-sided dice.\n",
			roll, dice, sides);
	}
	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;
}

分配内存:malloc()和free()

/* dym_arr.c ---动态分配数组 */
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>

int main(void)
{
    
	double* ptd;
	int max;
	int number;
	int i = 0;

	puts("What is the maximum number of type double entries?");
	if (scanf("%d", &max) != 1) {
    
		puts("Number not correct entered -- bye.");
		exit(EXIT_FAILURE);
	}
	ptd = (double*)malloc(max * sizeof(double));
	if (ptd == NULL) {
    
		puts("Memory allocation failed. Goodbye.");
		exit(EXIT_FAILURE);
	}
	/* ptd现在指向有max个元素的数组 */
	puts("Enter the values (q to quit):");
	while (i < max && scanf("%lf", &ptd[i]) == 1) {
    
		++i;
	}

	printf("Here are your %d entries:\n", number = i);
	for (i = 0; i < number; i++) {
    
		printf("%7.2f ", ptd[i]);
		if (i % 7 == 6) {
    
			putchar('\n');
		}
	}
	if (i % 7 != 0) {
    
		putchar('\n');
	}
	puts("Done.");
	free(ptd);

	return 0;
}