1、不使用全局变量，重写程序清单12.4中的程序。
#include <stdio.h>
void critic(int*);
int main(void)
{
int units = 0;
printf("How many pounds to a firkin of butter?\n");
scanf("%d", &units);
while ( units != 56)
critic(&units);
printf("You must have looked it up!\n");
return 0;
}
void critic(int *p)
{
printf("No luck, chummy. Try again.\n");
scanf("%d", p);
}
2、在美国通常是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（公制的或美制的），然后收集数据来计算油耗。
#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 quit): ");
scanf("%d", &mode);
}
printf("Done.\n");
return 0;
}
下面是一些输出示例：
Enter 0 for metric mode, 1 for US mode: 0
Enter distance traveled in kilometers: 600
Enter fuel consumed in liters: 78.8
Fuel consumption is 13.13 liters per 100 km.
Enter 0 for metric mode, 1 for US mode (-1 to quit): 1
Enter distance traveled in miles: 434
Enter fuel consumed in gallons: 12.7
Fuel consumption is 34.2 miles per gallon.
Enter 0 for metric mode, 1 for US mode (-1 to quit): 3
Invalid mode specified. Mode 1(US) used.
Enter distance traveled in miles: 388
Enter fuel consumed in gallons: 15.3
Fuel consumption is 25.4 miles per gallon.
Enter 0 for metric mode, 1 for US mode (-1 to quit): -1
Done.
如果用户键入了不正确的模式，程序向用户给出提示信息并选取最接近的模式。请提供一个头文件pe12-2a.h和源代码文件pe12-2a.c，来使程序可以运行。源代码文件应定义3个具有文件作用域、内部链接的变量。一个代表模式，一个代表距离，还有一个代表消耗的燃料。函数get_info()根据模式设置提示输入相应的数据，并将用户的回答存入文件作用域变量。函数show_info()根据所选的模式计算并显示燃料消耗值。
//pe12-2a.c
#include <stdio.h>
#include "pe12-2a.h"
static int present_mode = METRIC;
static double distance;
static double fuel;
void set_mode(int mode)
{
if (mode==METRIC || mode==US)
present_mode = mode;
else
printf("Invalid mode specified. Mode %s used.\n", present_mode == METRIC? "0(METRIC)" : "1(US)");
}
void get_info(void)
{
if (present_mode==METRIC)
{
printf ("Enter distance traveled in kilometers:");
scanf ("%lf",&distance);
printf ("Enter fuel consumed in liters:");
scanf ("%lf",&fuel);
}
else
{
printf ("Enter distance traveled in miles:");
scanf ("%lf",&distance);
printf ("Enter fuel consumed in gallons:");
scanf ("%lf",&fuel);
}
}
void show_info(void)
{
if (present_mode==METRIC)
printf ("Fuel consumption is %g liters per 100 km.\n", fuel / (distance/100) );
else
printf ("Fuel consumption is %g 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 quit): ");
scanf ("%d",&mode);
}
printf ("Done.\n");
return 0;
}
3、重新设计练习2中的程序，使它仅使用自动变量。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等。然而，您还必须给出一组不同的函数调用。
//pe12-3a.c
#include <stdio.h>
#include "pe12-3a.h"
void set_mode(int mode, int *p_present_mode)
{
if (mode==METRIC || mode==US)
*p_present_mode = mode;
else
printf("Invalid mode specified. Mode %s used.\n", *p_present_mode == METRIC? "0(METRIC)" : "1(US)");
}
void get_info(int mode, int present_mode, double *p_disance, double *p_fuel)
{
if (present_mode==METRIC)
{
printf ("Enter distance traveled in kilometers:");
scanf ("%lf",p_disance);
printf ("Enter fuel consumed in liters:");
scanf ("%lf",p_fuel);
}
else
{
printf ("Enter distance traveled in miles:");
scanf ("%lf",p_disance);
printf ("Enter fuel consumed in gallons:");
scanf ("%lf",p_fuel);
}
}
void show_info(int present_mode, double distance, double fuel)
{
if (present_mode==METRIC)
printf ("Fuel consumption is %g liters per 100 km.\n", fuel / (distance/100) );
else
printf ("Fuel consumption is %g miles per gallon.\n", distance / fuel );
}
//pe12-3b.c
#include <stdio.h>
#include "pe12-3a.h"
int main(void)
{
int mode,present_mode = METRIC;
double distance,fuel;
printf ("Enter 0 for metric mode.1 for US mode: ");
scanf ("%d",&mode);
while (mode >= 0)
{
set_mode (mode,&present_mode);
get_info (mode, present_mode, &distance, &fuel);
show_info (present_mode, distance, fuel);
printf ("Enter 0 for metric mode.1 for US mode:");
printf(" (-1 to quit): ");
scanf ("%d",&mode);
}
printf ("Done.\n");
return 0;
}
//pe12-3a.h
#define METRIC 0
#define US 1
void set_mode(int mode, int *present_mode);
void get_info(int mode, int present_mode, double *p_disance, double *p_fuel);
void show_info(int present_mode, double distance, double fuel);
4、编写—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之。
#include <stdio.h>
int Fibonacci(int n);
int count;
int main(void)
{
int n;
printf("input the max term of Fibonacci:");
while( scanf("%d",&n) == 1 )
{
count = 0;
Fibonacci(n);
printf("The function of Fibonacci has call %d times\n",count);
printf("input the max term of Fibonacci:");
}
puts("Quit");
return 0;
}
int Fibonacci(int n)
{
count++;
if( n>2 )
return Fibonacci(n-1) + Fibonacci(n-2);
else
return 1;
}
5、编写产生100个l到10范围内的随机数的程序，并且以降序排序（可以将11章中的排序算法稍加改动来对整数进行排序。这里，对数字本身进行排序即可）。
#include <stdio.h>
#include <stdlib.h>
#define WIDTH 100
int main(void)
{
char num[WIDTH],i,j,temp;
for(i=0; i<WIDTH; i++)
num[i] = rand() % 10 + 1;
printf("Original\n");
for(i=0; i<WIDTH; i++)
{
printf("%d\t",num[i]);
// if(i == 9) printf("\n");
}
printf("Sort:\n");
for(i=0; i<WIDTH-1; i++)
for(j=0; j<WIDTH-1-i; j++)
if (num[j] < num[j+1])
{
temp = num[j];
num[j] = num[j+1];
num[j+1] = temp;
}
for(i=0; i<WIDTH; i++)
{
printf("%d\t",num[i]);
// if(i == 9) printf("\n");
}
return 0;
}
6、编写一个产生1000个l到10范围内的随机数的程序。不必保存或打印数字，仅打印每个数被产生了多少次。让程序对10个不同的种子值进行计算。数字出现的次数相同吗？可以使用本章中的函数或ANSIC中的函数rand()和srand()，它们与我们的函数具有相同的形式。这是一个测试特定随机数发生器的随机性的方法。
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char i,seed[10]={0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
int j,count[10];//存放1~10的10个统计量
for (i=0; i<10;i++)
{
for (j=0; j<10; j++)
count[j] = 0;
srand(seed[i]);
for (j=0; j<1000; j++)
count[ rand() ]++;
printf("seed = %d:\n",seed[i]);
for (j=0; j<10; j++)
printf("%d: %d times:\t",j+1,count[j]);
printf("\n");
}
return 0;
}
7、编写一个程序，该程序与我们在显示程序清单12.13的输出之后所讨论的修改版程序具有相同表现。也就是说，输出应像下面这样：
Enter the number of sets; enter q to stop.
18
How many sides and how many dice?
6 3
Here are 18 sets of 3 6-sided throws.
12 10 6 9 8 14 8 15 9 14 12 17 11 7 10
13 8 14
How many sets? Enter q to stop.
q
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(void)
{
char set,side,dice,i,sum;
puts("Enter the number of sets:enter q to stop");
while(scanf("%d",&set) == 1)
{
srand( time(0) );
puts("How many sides and how many dice?");
while(scanf("%d%d", &side, &dice) != 2)
{
scanf("%*s");//滤除非法输入
printf("input error! input again:");
}
printf ("Here are %d sets of %d %d-sided throws.\n",set, dice, side);
while (set--)
{
for (i=0,sum=0; i<dice; i++)
sum += rand() % side +1;
printf("\t%d",sum);
}
puts("\nHow many sets?enter q to stop");
}
return 0;
}
下面是某程序的一部分：
// pe12-8.c
#include <stdio.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: ");
scanf("%d", &size);
while (size > 0)
{
printf("Enter the initialization 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;
}
8、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内容。
#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:");
scanf ("%d", &size);
while (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):");
scanf("%d", &size);
}
printf("Done.\n");
return 0;
}
int * make_array (int elem, int val)
{
int *p;
p = (int *)malloc( elem * sizeof(int) );
while(elem--)
*(p + elem) = val;
return p;
}
void show_array (const int ar[], int n)
{
int i;
for (i=0;i<n;i++)
{
printf("%d\t",ar[i]);
if(i%8==7) printf("\n");
}
}
