C final review

1. Direct access is to access directly by using the address of the variable .(T)

analysis ：

（1） Direct access :

Access the variable value according to the address of the variable .

（2） Indirect access to :

Access variables through variables that store variable addresses .

2. Let the variable be defined as int a[2]={1,3}, *p=&a[0]+1; be *p The value of is ( 3 ).

analysis ： Notice the address plus one , instead of It's worth adding 1;

3. For the following structure definitions ,++p->str Medium ++ Add to （A）.

struct {
   int len; 
   char *str; 
} *p;

A. The pointer str On   B. The pointer p On    C.str Point to the content    D. Grammar mistakes

4.C Structure type variables in the language during program execution （ All members always reside in memory ）.

5. What linked lists don't have is （ Any element can be accessed at random ）.

6. When using linked list instead of array for data operation , Query is more convenient .（F）

analysis ：

Array : Support random access , Easy to use , Query efficiency is higher than linked list , Memory It is a continuous area .
Linked list ： No data access , Can be dynamically added or deleted Variable size , Memory may be discontinuous , Chain store , Query efficiency is low . 

7. stay C In the program , Functions can be either nested or defined , You can also nest calls .（F)

analysis ：

C The definitions of functions in language are parallel to each other 、 Mutually independent , That is to say, when defining a function , A function body cannot contain the definition of another function , That is, functions cannot be nested , But you can nest calls .

8. The file pointer points to the access location of the file data in the file buffer .（F）

analysis ：

The file pointer points to A memory area , This area stores information about the open file , Including the current position of the file reading pointer 、 File read buffer size and other information , Not pointing to a file .

9. Using a structure pointer as a function parameter only needs to pass an address value , therefore , It can improve the efficiency of parameter transmission .（T）

10. Known and defined ,FILE fp; char str[] = "Good！"; fp = fopen("filename.dat", "wb");
Will array str The string stored in is written to the name filename.dat In the binary file of . The required statement is ( D).

A.fwrite(str[0], sizeof(char), 1, fp)                                         B.fread(str, sizeof(char), 5, fp)

C.fwrite(fp, sizeof(char), 5, str)                                             D.fwrite(str, sizeof(char), 5, fp)

analysis ：

fread And fwrite function

The function prototype ：
size_t fread(void *buffer, size_t size, size_t, count, FILE *pf)
size_t fwrite(void *buffer, size_t size, size_t count, FILE *pf)

fread and fwrite Function is generally used for input and output of binary files .

fscanf And fprintf function

for example ：

fscanf(fp, "%s %d %d %f\n", pb->name, &pb->num, &pb->age, &pb->score)

fprintf(fp,"%s %d %d %f\n", pa->name, pa->num, pa->age, pa->score)

fscanf The function ：

Press “ Format string ” Specified format , from “ File type pointer ” Read data from the current location of the file pointed to , Then press “ Entry address table column ” The order of , Store the read data into the specified memory unit .

fprintf The function ：

Press “ Format string ” Specified format , take “ Output item table column ” Write the values of the items specified in “ File type pointer ” The current location of the file pointed to . If the write is successful ,fprintf The return value of the function is the number of characters written to the file （ Or number of bytes ）, Otherwise return to EOF（-1）.

11. Open a text file for student.txt, The correct way to add data is ( B ).

A.fp=fopen("my.txt","r")                           B.fp=fopen("my.txt","a")

C.fp=fopen("my.txt","w")                         D.fp=fopen("my.txt","w+")

r  With read-only Way to open a file . The pointer to the file will be placed at the beginning of the file . This is the default mode .

a     Open a file for Additional . If the file already exists , The file pointer will be placed at the end of the file . in other words , The new content will be written after the existing content . If the file does not exist , Create a new file to write to .

a+     Open a file For reading and writing only . If the file already exists , The file pointer will be placed at the end of the file . Append mode when the file opens . If the file does not exist , Create a new file for reading and writing .

w     Open a file Write only . Open the file if it already exists , And edit from the beginning , The original content will be deleted . If the file does not exist , Create a new file .

w+     Open a file for Reading and writing . Open the file if it already exists , And edit from the beginning , The original content will be deleted . If the file does not exist , Create a new file .

wb     With Binary format Open a file Write only . Open the file if it already exists , And edit from the beginning , The original content will be deleted . If the file does not exist , Create a new file . Generally used for non - text files such as pictures .

wb+     With Binary format Open a file For reading and writing . Open the file if it already exists , And edit from the beginning , The original content will be deleted . If the file does not exist , Create a new file . Generally used for non - text files such as pictures .

12.

The following description is wrong ( D ).

A. Function calls can appear in an expression                               B. Function calls can appear in the execution statement

C. Function calls can be used as arguments to a function                               D. Function calls can be used as formal parameters of a function

analysis ：

The return value is stored in the register , No address , It cannot be a formal parameter , But it can be used as an argument .