Final answer:
The fopen() function takes two arguments: the filename and the mode in which to open the file, such as "r" for reading or "w" for writing.
Step-by-step explanation:
The function fopen() in C programming is used to open a file and it takes two arguments. The first argument is a string that represents the name of the file to be opened. The second argument is a string that represents the mode in which to open the file. There are several different modes that can be used, such as "r" for reading, "w" for writing, "a" for appending, and more. These modes specify how you intend to use the file and consequently affect the behavior of the function with respect to the file.