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>> SPEAKER: Up until now, in programs we've
written, we've declared main as

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int main void.

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And all this time, that void has
simply been specifying that the

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program does not take any
command line arguments.

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In other words, when a user runs a
program, he or she can provide command

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line arguments by writing additional
words or phrases after the program's

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name at the prompt.

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>> Well, if you do want your program to
take command line arguments, one or

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more such words, we need to replace
void with a couple of arguments.

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So let's do that.

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Include CS50.h.

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Include standard io.h.

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Int, main, and now instead of void,
I'm going to specify an int called

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argc, and an array of
strings called argv.

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>> Now, argc and argv are
simply conventions.

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We could've call these arguments
most anything we want.

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But what is important is that argc is
an int, because by definition, it is

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going to contain the argument counts,
the number of words in total that the

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user has typed at his or her prompt.

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>> Argv, meanwhile, argument vector, is
going to actually be an array storing

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all of the words that the user has
typed at his or her prompt.

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Let's proceed to do something now
with one or more of these

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command line arguments.

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In particular, let's go ahead and print
whatever word the user types

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after the program's name
at the prompt.

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>> Open bracket, closed bracket, print
f, percent s, backslash n, comma.

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And now I need to tell print f what
value to plug into that placeholder.

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I want the first word that the user has
typed after the program's name.

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And so I'm going to specify
argv bracket 1, closed

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parenthesis, semicolon.

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>> Now, why bracket 1 and not bracket 0?

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Well, it turns out, automatically stored
in argv 0 is going to be the

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program's actual name.

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So the first word that the user types
after the program's name is, by

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convention, going to be
stored in argv 1.

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>> Let's now compile and
run this program.

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Make argv 0 dot slash argv 0, and
now a word like hello, enter.

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And there we have it, hello.

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