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 <stdio.h>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 <stdio.h># 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 <stdio.h># 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 <stdio.h>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 <stdio.h>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 <stdio.h># include <stdlib.h>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 <stdio.h># include <stdlib.h>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 <stdio.h># include <stdlib.h># include <time.h>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 <stdio.h># include <stdlib.h># include <malloc.h>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");    }}