The following C expression can be substituted for?

if (isalpha(c) && isdigit(c))

In C, which library is used for file operations such as reading and writing files?

A. stdio.h

B. iostream.h

C. fileio.h

D. files.h

Which function is used to open a file in C for writing?

A. fopen()

B. open()

C. writefile()

D. createfile()

What does 'FILE' represent in C when working with files?

A. A built-in data type for files

B. A file descriptor

C. A file pointer

D. A file structure

How do you check if a file was opened successfully in C?

A. Use the 'filestatus' variable

B. Check the return value of fopen()

C. Use the 'fileopen' function

D. Check the file's size