What do argc and argv have to do with the subject of cryptography? Nothing.
But they DO have a lot to do with how you get data into a program when it is started. Just in case you didn't comprehend it, here's what those two items do.
argc is a built-in variable in C, one of the few. It tells the program the number of parameters that were in the call to the program. It will always be at least 1. (I'll explain shortly.)
argv is an array. Specifically, it is an array of strings. Each string is a char array in itself. The argv array will always have at least one element. That element is argv, and will contain the string that started the program. Each element of the array that follows will be a parameter in the command line.
For example, say that you execute the following program:
./foobar test 21 "I'm a program"
This will cause argc to be set to 4 and the argv array will be:
I'm a program
Each of these is a string. Note in particular that argv is not an int or any kind of number. It's the string containing two characters, 2 and 1. Next, argv is also a string, but it contains spaces. Since it was put in quotes, it was treated as one string, not 3 strings separated by spaces.
Now, why was it presented in the lecture as it was? It's time to present the standard format of creating a main() program and to teach how to pass data into the program at execution call time. It has to be presented now.
Also, you're getting a lot of information thrown at you at once. It's going to be like trying to drink water from a fire hose! Time to get used to it! ;-)
If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)