记录——《C Primer Plus （第五版）》第十二章编程练习第1-8题

1.不使用全局变量，重写12.4的程序 。

# include 

int critic(void);
int main(void)
{
    int units = 0;

    printf("How many pounds to a firkin of butter?\n");
    scanf("%d", &units);

    while(units != 56)
    {
        units = critic();
    }

    printf("You must have looked it up!\n");

    return 0;
}

int critic(void)
{
    int units = 0;
    printf("No luck,chumy.Try again.\n");
    scanf("%d", &units);

    return units;
}

2.在美国通常以英里每加仑来计算油耗，在欧洲是以升每百公里来计算，下面是某程序的一部分，该 程序让用户选择一个模式（公制和美制），然后收集数据来计算油耗。

pe2a.c
# include 
# include "pe2a.h"

static int model = 0;
static float distance = 0;
static float fuel = 0;

void set_mode(int mode)
{
    model = mode;
    return;
}

void get_info(void)
{
    extern int model;
    extern float distance;
    extern float fuel;

    if(0 == model)
    {
        printf("Enter distance traveled in kilometers: ");
        scanf("%f", &distance);
        printf("Enter fuel consumed in liters: ");
        scanf("%f", &fuel);
    }
    else if(1 == model)
    {
        printf("Enter distance traveled in kilometers: ");
        scanf("%f", &distance);
        printf("Enter fuel consumed in gallons: ");
        scanf("%f", &fuel);
    }
}

void show_info(void)
{
    extern int model;
    extern float distance;
    extern float fuel;

    if(0 == model)
    {
        printf("Fuel consumption is %.2f liters per 100 km.\n", 100*fuel/distance);
    }
    else if(1 == model)
    {
        printf("Fuel consumption is %.2f miles per gallon.\n", fuel/distance);
    }
}

pe2b.c
# include 
# include "pe2a.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 quit): ");
        scanf("%d", &mode);
    }
    printf("Done.\n");

    return 0;
}

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

3.重新设计练习二，使用自动变量，程序提供相同的用户界面，也就是说，要提示用户输入模式等。

# include 

float get_info(int);
void show_info(int, float);

 int model = 0;
 float distance = 0;
float fuel = 0;

int main(void)
{
    int model = 0;
    float unit_fuel = 0;

    printf("-----------------油耗计算-----------------\n");
    printf("模式         模式内容\n");
    printf("  0          以升每百公里 \n");
    printf("  1          以加仑每英里\n");
    printf(" -1          退出\n");
    printf("------------------------------------------\n");
    printf("Enter 0 for metric mode, 1 for us mode: ");
    scanf("%d", &model);
    while(model >= 0)
    {
        unit_fuel = get_info(model);
        show_info(model, unit_fuel);
        printf("\n-----------------油耗计算-----------------\n");
        printf("模式         模式内容\n");
        printf("  0          以升每百公里 \n");       
        printf("  1          以加仑每英里\n");
        printf(" -1          退出\n");
        printf("------------------------------------------\n");
        printf("Enter 0 for metric mode, 1 for us mode");
        printf("(-1 to quit): ");
        scanf("%d", &model);
    }
    printf("Done.\n");

    return 0;
}


float get_info(int model)
{
    float distance;
    float fuel;
    float unit_fuel;
    if(0 == model)
    {
        printf("Enter distance traveled in kilometers: ");
        scanf("%f", &distance);
        printf("Enter fuel consumed in liters: ");
        scanf("%f", &fuel);
        unit_fuel = 100*fuel/distance;
    }
    else if(1 == model)
    {
        printf("Enter distance traveled in kilometers: ");
        scanf("%f", &distance);
        printf("Enter fuel consumed in gallons: ");
        scanf("%f", &fuel);
        unit_fuel = fuel/distance;
    }
    return unit_fuel;
}

void show_info(int model, float unit_fuel)
{
    if(0 == model)
    {
        printf("Fuel consumption is %.2f liters per 100 km.\n", unit_fuel);
    }
    else if(1 == model)
    {
        printf("Fuel consumption is %.2f miles per gallon.\n", unit_fuel);
    }
}

3.编写一个函数，它返回函数自身被调用的次数，并在一个循环中测试

# include 

static int i;
int f(int n);
int main(void)
{
    int i = 0;
    printf("请输入循环次数(输入0退出程序)：");
    scanf("%d", &i);
    while(i != 0)
    {
        printf("%d\n", f(i));
        printf("请输入循环次数(输入0退出程序)：");
        scanf("%d", &i);
    }
    return 0;
}

int f(int n)
{
    extern int i;
    i = 0;
    if(0 != n)
    {
        f(n-1);
        i++;
    }
    return i;
}

5.编写产生100个1到10范围的随机数，并且以降序排序。

# include 
# include 

void init(int *rands);
void descending_sort(int *rands);
void show(int *rands);
int main(void)
{
    int rands[100] = {0};

    init(rands);
    descending_sort(rands);
    show(rands);
    return 0;
}

void init(int *rands)
{
    int num;
    for(int i = 0; i < 100; i++)
    {
        num = rand() % 10 + 1;
        rands[i] = num;
    }
}

void descending_sort(int *rands)
{
    int num;
    for(int i = 0; i < 99; i++)
    {
        for(int j = i; j < 99; j++)
        {
            if(rands[i] < rands[j+1])
            {
                num = rands[i];
                rands[i] = rands[j+1];
                rands[j+1] = num;

            }
        }
    }
}

void show(int *rands)
{
    for(int i = 0; i < 100; i++)
    {
        printf("%3d ", rands[i]);
        if(0 == (i+1) % 10)
            printf("\n");
    }
}

6 编写产生1000个1到10范围的随机数,并统计每个数产生的次数 .

# include 
# include 

int main(void)
{
    int num;
    int randomness[10] = {0};  //数组装1-10出现的次数

    for(int i = 0; i < 1000; i++)
    {
        num = rand() % 10 + 1;
        switch (num)
        {
        case 1:
            randomness[0] += 1;
            break;
        case 2:
            randomness[1] += 1;
            break;
        case 3:
            randomness[2] += 1;
            break;
        case 4:
            randomness[3] += 1;
            break;
        case 5:
            randomness[4] += 1;
            break;
        case 6:
            randomness[5] += 1;
            break;
        case 7:
            randomness[6] += 1;
            break;
        case 8:
            randomness[7] += 1;
            break;
        case 9:
            randomness[8] += 1;
            break;
        case 10:
            randomness[9] += 1;
            break;
        }
    }   
    for(int j  = 0; j < 10; j++)
        printf("%3d 出现的次数 %d\n", j+1, randomness[j]);

    return 0;
}

7.编写一个程序，该程序与我们在显示程序清单12.13输出之后所讨论的修改程序具有相同的表现，也就是说，输出应像下面这样：
Enter the number of sets,enter q to stop.
How many sides and how many dice?
Here are 18 sets of 3 6-sided throws：
11 7 10 11 10 15 13 9 12 13 11 9 8 12 8
16 7 9
Enter the number of sets,enter q to stop.
*/

# include 
# include 
# include 

int roll_count = 0;
int rollem(int sides);
int roll_n_dice(int dice, int sides);
int main(void)
{
    int dice, roll;
    int sides;
    int num;
    int i;

    srand((unsigned int) time(0));
    printf("Enter the number of sets: enter q to stop.");
    scanf("%d", &num);
    printf("How many sides?\n");
    while(scanf("%d", &sides) == 1 && sides > 0)
    {
        printf("How many dice?\n");
        scanf("%d", &dice);
        printf("Here are %d sets of %d %d-sides throws.", num, sides, dice);
        for(i = 0; i < num; i++)
        {
            roll = roll_n_dice(dice, sides);
            printf("%d  ", roll);
        }
        printf("\nHow many sides? Enter 0 to stop.\n");
    }
    printf("The rollem() function was called %d times.\n", roll_count);
    printf("GOOD FORTUNE TO YOU!\n");
    return 0;
}

int rollem(int sides)
{
    int roll;

    roll = rand() % sides +1;
    ++roll_count;
    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;
}

8.下面是某程序的一部份，给出函数make_array()和show_array()的定义以使程序完整。函数make_array()接受两个参数。
第一个是int数组的元素个数，第二个是要赋给每个元素的值。函数使用malloc()来创建一个适当大小的数组，把每个元素设定 为指定的值，并返回一个数组指针，函数show_array()以8个数一行的格式显示数组的内容。

# include 
# include 
# include 

int *make_array(int elem, int val);
void show_array(const int arr[], int n);

int main(void)
{
    int * pa;
    int size;int value;

    printf("Enter the number of elements: ");
    scanf("%d", &size);
    while(size > 0)
    {
        printf("Enter the intitialization value: ");
        scanf("%d", &value);
        pa = make_array(size, value);
        if (pa)
        {
            show_array(pa, size);
            free(pa);
        }
        printf("Enter the number of elements(<1 to quit): ");
        scanf("%d", &size);
    }
    printf("Done.\n");

    return 0;
}

int * make_array(int elem, int val)
{
    int * p;
    p = (int *)malloc(sizeof(int) * elem);
    for(int i = 0; i < elem; i++)
    {
        p[i] = val;
    }

    return p;
}

void show_array(const int arr[], int n)
{
    for(int i = 0; i < n; i++)
    {
        printf("%d  ", arr[i]);
        if(0 == (i+1) % 8)
        printf("\n");
    }
}