1.
16.
（c）(e)正确。
（a）数字太大时会出问题。
（b）错误的主要原因是枚举enum和用#define指令创建的常量相比，枚举遵循C语言的作用域规则：如果枚举声明在函数体内，那么它的常量对外部函数来说是不可见的。
（d）没有必然要求，可以相同。
21.
（a）enum {NUL,SOH,STX,ETX};
NUL = 0,SOH = 1,STX = 2,ETX = 3.
（b）enum {VT = 11,FF,CR}
VT = 11, FF = 12, CR = 13
（c）enum {SO = 14,SI,DLE,CAN = 24,EM}
SO = 14,SI = 15,DLE = 16,CAN = 24,EM = 25
（d）enum {ENQ = 45,ACK,BEL,LF = 37,ETB,ESC}
ENQ = 45,ACK = 46,BEL = 47,LF = 37,ETB = 38, ESC = 39
2.
/*有序插入建立链表 C语言实现*/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 100000
/*定义一个linklist结构体类型*/
typedef struct linklist
{
char name;
int student_id;
int grade;
struct linklist *next;
}list, *plist;
/*按从小到大顺序插入*/
void order_insert_list(plist *head)
{
plist p_new = (plist)malloc(sizeof(list));
plist pre = NULL;
p_new->name = 'a'+rand()%26;
p_new->student_id = rand(); /* pre指针作为temp指向next前的备份 */
p_new->grade = rand(); /* 赋予新值给新结点 */
p_new->next = NULL;
plist temp = (plist)malloc(sizeof(list));
temp = *head; /*每次插入前从链表头开始的位置*/
/*首位空结点赋初值*/
if (NULL == *head)
{
*head = p_new;
return;
}
/*若新data比头结点小，头结点前插入*/
if (p_new->grade < temp->grade)
{
p_new->next = temp;
*head = p_new;
return;
}
else
{
while (NULL != temp)
{
if (p_new->grade >= temp->grade)/* 新结点对当前结点data比较 */
{
pre = temp;
temp= temp->next;/*当前结点后移，直至5（比如1 2 3 5 插入4）的位置*/
continue;
}
else
{
p_new->next = temp;/* 插入新结点 */
pre->next = p_new; /* temp的前一个的位置的next指向新结点p_new */
break;
}
}
if (NULL == temp)/* 当temp最终为尾结点时，说明新元素data最大，将结点作为尾结点 */
{
p_new->next = NULL;
pre->next = p_new; /* temp的前一个的位置的next指向新结点p_new */
}
}
}
void print_list(plist head)
{
plist elem = head;
while (elem != NULL)
{
printf("%d %d %c\n", elem->grade,elem->student_id,elem->name);
elem = elem->next;
}
printf("\n");
}
int main()
{
int start = time(NULL);
srand(time(NULL));
plist head; /*定义表头*/
head = NULL;
//printf("input some numbers:\n");
for(int i=0;i<N;i++){
order_insert_list(&head);
}
//print_list(head);/*打印输出*/
int end =time(NULL)-start;
printf("Program execution time is %d",end);
return 0;
}
PS E:\vscode-c\build> cd "e:\vscode-c\build\" ; if ($?) { gcc link_list_order1.c -o link_list_order1 } ; if ($?) { .\link_list_order1 }
when N = 10000, Program execution time is 0
PS E:\vscode-c\build> cd "e:\vscode-c\build\" ; if ($?) { gcc link_list_order1.c -o link_list_order1 } ; if ($?) { .\link_list_order1 }
when N = 30000, Program execution time is 3
PS E:\vscode-c\build> cd "e:\vscode-c\build\" ; if ($?) { gcc link_list_order1.c -o link_list_order1 } ; if ($?) { .\link_list_order1 }
when N = 50000, Program execution time is 8
PS E:\vscode-c\build> cd "e:\vscode-c\build\" ; if ($?) { gcc link_list_order1.c -o link_list_order1 } ; if ($?) { .\link_list_order1 }
when N = 80000, Program execution time is 31
PS E:\vscode-c\build> cd "e:\vscode-c\build\" ; if ($?) { gcc link_list_order1.c -o link_list_order1 } ; if ($?) { .\link_list_order1 }
when N = 100000, Program execution time is 98
可以看出随着N的增大，程序的执行时间不断增大而且幅度很大，所以构建有序列表会耗费大量时间，但反而有序列表会使得检索比较方便，从而在检索时节省大量时间。
3.
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#define N 30000
struct node{
int value;
struct node *next;
};
int get_list_node_len(struct node *list){
int len = 0;
while(list!=NULL){
list = list->next;
len++;
}
return len;
}
struct node *search_list(struct node *list,int len,int L){
if(len<L){
printf("len < L !");
return list;
}else{
for(int i=0;i<len-L;i++){
list = list->next;
}
return list;
}
};
struct node *add_to_list(struct node *list,int n)
{
struct node *new_node;
new_node = malloc(sizeof(struct node));
if(new_node == NULL){
printf("Error:malloc failed in add_to list\n");
exit(1);
}
new_node->value = n;
new_node->next = list;
return new_node;
};
struct node *initial(struct node *list){
int n;
//struct node *first = NULL;
for(int i=0;i<N+rand()%1000;i++){
n = rand();
//printf("%d\n",n);
if(n==0) break;
list = add_to_list(list,n);
//printf("the node of list is %d\n",get_list_node_len(list));
}
return list;
}
void print_list(struct node *list){
while (list!= NULL){
printf("%d\n", list->value);
list = list->next;
}
printf("\n");
}
int main(){
int L;
struct node *first = NULL;
srand(time(NULL));
first = initial(first);
int length = get_list_node_len(first);
printf("enter the L:");
scanf("%d",&L);
printf("the length is %d,the L is %d\n",length,L);
struct node *list = search_list(first,length,L);
printf("the penultimate %d node is %d\n",L,list->value);
//print_list(first);
//print_list(list);
return 0;
}
4.
16.
#include <stdio.h>
int g(int);
int sum(int (*f)(int),int start, int end);
int main(){
int i,j;
printf("enter two numbers:");
scanf("%d %d",&i,&j);
printf("the result is %d",sum(g,i,j));
return 0;
}
int g(int x){
return x*x;
}
int sum(int (*g)(int),int start, int end){
int sum;
for(int i=start;i<=end;i++){
sum += g(i);
}
return sum;
}
5.
14.
#define N = 10
#define INC(x) x+1
#define SUB(x,y) x - y
#define SQR(x) ((x)*(x))
#define CUBE(x) (SQR(x)*(x))
#define M1(x,y) x##y
#define M2(x,y) #x #y
int main(){
int a[N],i,j,k,m;
#ifdef N
i = j;
#else
j = i;
#endif
i = 10 *INC(j);
i = SUB(j,k);
i = SQR(SQR(j));
i = CUBE(j);
i = M1(j,k);
puts(M2(i,j));
#undef SQR
i = SQR(j);
#define SQR
i = SQR(j);
return 0;
}
有三处错误。
第1行有错，应删去 “=”。
第23行有错， i = M1(j,k);将jk连接在一起导致未定义的行为。
第26行有错，#undef 取消了对于SQR的定义，之后又使用了宏SQR导致错误。
Blank line
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int main(void)
{
int a[= 10], i, j, k, m;
Blank line
i = j;
Blank line
Blank line
Blank line
i = 10 * j+1;
i = (x,y) x-y(j, k);
i = ((((j)*(j)))*(((j)*(j))));
i = (((j)*(j))*(j));
i = jk;
puts("i" "j");
Blank line
i = SQR(j);
Blank line
i = (j);
return 0;
gcc编译器可以使用-E来查看预处理之后的输出。
在cmd命令行环境下输入gcc -E macro_error.c -o macro，会产生macro文件，使用记事本打开之后就会看到预处理器的输出。
15.
#include <stdio.h>
#define ENGLISH
#define FRENCH
#define SPANISH
int main(){
#ifdef ENGLISH
printf("Insert Disk 1\n");
#endif
#ifdef FRENCH
printf("Insert LeDisq 1\n");
#endif
#ifdef SPANISH
printf("Insert El Disco\n");
#endif
return 0;
}
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