💻 Unit 5 – Part A (2-Mark Q&A)

33. What is meant by command line argument?

Command-line arguments are values (strings) passed to a C program when it is executed from the command line or terminal. They are accessed in the main() function using the argc (argument count) and argv (argument vector) parameters.

34. How do you open a file in C for reading and writing?

You can open an existing file for both reading and writing using the "r+" mode with the fopen() function. If the file doesn't exist, it will return NULL.

Example: FILE *fp = fopen("data.txt", "r+");

35. Why preprocessor directives are used?

Preprocessor directives are instructions to the C preprocessor (which runs before the actual compiler). They are used for:

• #include: To include header files (libraries).
• #define: To define macros and symbolic constants.
• #if, #else, #endif: For conditional compilation (compiling parts of the code only if a condition is met).

36. What does argc and argv indicate in command-line arguments?

• argc (Argument Count): An integer that stores the total number of command-line arguments passed to the program, including the program name itself.
• argv (Argument Vector): An array of character pointers (char *argv[]) where each element points to a string. argv[0] is the program name, argv[1] is the first argument, and so on.

37. Brief about single line comment with example.

A single-line comment is used to add explanatory notes to the code, which are ignored by the compiler. In C (from C99 standard), it starts with // and continues to the end of the line.

Example:

int x = 10; // This is a single-line comment initializing x.

38. How to open a file and close a file in C language?

• Open a file: Use the fopen() function, which returns a file pointer (FILE*). You must specify the filename and the mode (e.g., "r" for read, "w" for write).
  FILE *fp = fopen("filename.txt", "w");
• Close a file: Use the fclose() function, passing it the file pointer.
  fclose(fp);

39. What is meant by command line argument?

This is a duplicate of question 33. Command-line arguments are parameters supplied to a program when it is invoked from the command line. They provide a way to pass data into the program at runtime.

40. Compare the fseek() with ftell ().

• fseek(): This is a function used to move the file pointer (the current read/write position) to a specific location within a file (e.g., to the beginning, end, or a specific byte offset).
• ftell(): This is a function used to get the current position of the file pointer. It returns a long integer representing the number of bytes from the beginning of the file.