What is the purpose of "rb" in fopen() function used below in the code? FILE *fp; fp = fopen("source.txt", "rb");

The "rb" in the fopen() function stands for "read binary". This mode opens the file in binary mode for reading.

Here's a step-by-step explanation:

1. FILE *fp; - This line is declaring a pointer to a FILE. This is done because the fopen() function returns a pointer to the file that it opens.

2. fp = fopen("source.txt", "rb"); - This line is calling the fopen() function. The fopen() function is used to open a file.

3. "source.txt" - This is the name of the file that you want to open. It could be any valid file name.

4. "rb" - This is the mode in which you want to open the file. The "r" stands for "read", which means the file is opened for reading. The "b" stands for "binary", which means the file is opened in binary mode.

In binary mode, the file is read exactly as it is, without any transformations. This is important when reading non-text files like images or executable files, where any transformation of the data would result in corruption.