String and File Handling in C

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Questions and Answers

What is the return value of fclose() when a file is successfully closed?

NULL
1 (one)
0 (zero) (correct)
FILE pointer

What type should an array subscript be?

integer (correct)
double
character
float

Which function is used to write a string to a file in C?

putchar()
fputs() (correct)
getchar()
fwrite()

Which statement about arrays is true?

An array subscript must be an integer. (A) Signup and view all the answers

What does EOF signify in file handling?

End of a file (C) Signup and view all the answers

What is the primary purpose of a file pointer in C?

It defines properties of the file, such as name and status. (D) Signup and view all the answers

In the statement `FILE fp;`, what does the `` symbol represent?

A pointer to a variable of type FILE. (C) Signup and view all the answers

What does the expression `*var` reference in pointer terminology?

The contents of the memory location pointed to by the pointer. (A) Signup and view all the answers

What will happen if the file does not exist when trying to open it?

The file will be created for both reading and writing. (D) Signup and view all the answers

What does the variable `var` in the example code store?

The address of an integer variable. (D) Signup and view all the answers

When you declare a pointer as `int* var;`, what does this declaration imply?

The pointer can reference the address of an integer variable. (D) Signup and view all the answers

What is the significance of the memory address printed in the output of the example program?

It indicates the location where variable <code>num</code> is held in memory. (A) Signup and view all the answers

In the function `void main(void)`, what is the effect of `clrscr();`?

It clears the console screen. (A) Signup and view all the answers

What does the null character '\0' signify in a C string?

It signifies the end of the string. (D) Signup and view all the answers

What will happen if you try to assign a new string literal directly to an array variable in C?

An error will occur since it's not a single memory location. (C) Signup and view all the answers

Which C function is commonly used to copy strings from one variable to another?

strcpy (D) Signup and view all the answers

What would be the output if you tried to print a string stored as 'char name[16] =

The program will show an empty output or unknown behavior. (A) Signup and view all the answers

Which of the following statements about string assignment in C is correct?

You must use the strcpy function to assign a string to an array. (C) Signup and view all the answers

What will happen if you try to use the strcpy function with a destination buffer smaller than the source string size?

It may lead to a buffer overflow and undefined behavior. (C) Signup and view all the answers

What is the primary role of the string.h library in C?

It contains functions for string manipulation. (D) Signup and view all the answers

What is the correct way to declare a string variable in C?

char name[16]; (D) Signup and view all the answers

What does the last character in a C string represent?

The null terminator. (A) Signup and view all the answers

Which of the following statements correctly represents an array declaration in C?

int balls[6]; (B) Signup and view all the answers

What does 'n' represent in the array declaration 'data_type arr_name[n];'?

The total number of memory locations in the array. (D) Signup and view all the answers

Which of the following options can hold a string of 15 characters in C?

char name[16]; (B) Signup and view all the answers

When handling strings, why is it necessary to understand arrays in C?

Strings are implemented as an array of characters. (A) Signup and view all the answers

What is a common use of strings in programming as mentioned in the content?

To keep records of names and telephone numbers. (A) Signup and view all the answers

What type of variable can store a string in C?

char (D) Signup and view all the answers

What does the fputs() function do in C?

Writes a string to a file. (D) Signup and view all the answers

What is the return value of fputs() upon successful execution?

Non-negative value (B) Signup and view all the answers

What will happen if fgets() encounters an EOF before reading any characters?

It returns a null pointer. (B) Signup and view all the answers

Which of the following statements about the gets() function is true?

It does not store the newline character in the string. (D) Signup and view all the answers

What occurs in the program when an empty string is entered for the name?

The program terminates the input loop. (C) Signup and view all the answers

What should be noted about the size of the 'tel' array in the program?

It allows for 11 characters including the null terminator. (A) Signup and view all the answers

Why is a sentinel loop used in the program?

To terminate input based on user entry. (B) Signup and view all the answers

What happens to the null character in the string when using fputs()?

It is not written to the file. (C) Signup and view all the answers

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Study Notes

String Handling in C

Strings in C are implemented as arrays of characters.
A null terminator (\0) marks the end of a string.
Strings can be initialized using an array declaration:
- char name[16] = "Lahore";
String assignment is done by copying characters into the array using the strcpy() function:
- strcpy(name, "I love Pakistan");
The string.h library provides string manipulation functions in C.

File Handling in C

File operations involve reading and writing from/to files.
File Pointer: A variable of type FILE that points to a file. It stores information about the file including its name, status, and current position.
- Declaration Example: FILE *fp;

File Opening Modes

FILE *fopen(const char *filename, const char *mode); is used to open a file.
Modes for opening a file:
- r: Opens a file for reading.
- w: Opens a file for writing. Creates a new file if it doesn't exist, or overwrites an existing file.
- a: Opens a file for appending. Creates a new file if it doesn't exist.
- r+: Opens a file for both reading and writing.
- w+: Opens a file for both writing and reading. Creates a new file or overwrites an existing file.
- a+: Opens a file for both appending and reading.

File Input/Output Functions

fputs(char *str, FILE *fp): Writes a string (str) to the file associated with (fp).
fgets(char *str, int num, FILE *fp): Reads a string of characters from the file associated with (fp) into (str).
fclose(FILE *fp): Closes the file (fp) and frees any system resources used by it.
gets(char *str): Accepts a string from the keyboard and assigns it to (str).

Examples of C File Handling

Example 1: Demonstrates how to read strings from a file and store them in variables.
Example 2: Explains how to write strings to a file.
Example 3: Reads name and telephone number from the user and saves them in a text file.

Text and Binary Streams

Text Streams: Files treated as sequences of characters. Each character is represented by its ASCII code.
Binary Streams: Files treated as sequences of bytes. Each byte represents a piece of data in its binary form.

Important Notes

It is important to close files after using them to free up system resources.
When opening existing files in 'w' mode, their contents are overwritten.
Arrays are used to store data of the same type in contiguous memory locations.
Array subscript is used to access individual elements of an array.
EOF (End Of File) is a special character used in file handling to indicate the end of a file.
Binary files can store any type of data.

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