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write the name of the variable that you want
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to plug in into that format code, or format specifier,
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percent s for strings.
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And now if I've saved my file, I go back down to my terminal.
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And I type Make String, because, again, the name of this
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file that I chose before is string.c.
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>> So I'm going to say Make String, enter.
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Oh my goodness, look at all of the mistakes we've made already.
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And this is-- what, this is really like a six, seven line program?
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So this is where it can very quickly get overwhelming.
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>> This terminal window has now just regurgitated
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a huge number of error messages.
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Surely, I don't have more error messages than I have lines of code.
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So what is going on?
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>> Well, the best strategy to do anytime you
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do encounter an overwhelming list of errors like that,
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is scroll back, look for the command you just ran, which in my case
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is make string.
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Look at what make did, and that's that long Clang command, no big deal there.
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>> But the red is bad.
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Green is trying to be gentle and helpful.
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But it's still bad, in this case.
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But where is it bad?
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>> String.c, line five, character five.
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So this is just common convention.
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Something colon something means line number and character number.
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Error, use of undeclared identifier string.
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Did you mean standard in?
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>> So, unfortunately, Clang is trying to be helpful.
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But it's wrong, in this case.
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No, Clang, I did not mean standard IO.
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I meant that on line one, yes.
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>> But line five is this one here.
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And Clang does not understand S-T-R-I-N-G.
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It's an undeclared identifier, a word it just has never seen before.
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And that's because C, the language we're writing code in right now,
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does not have variables called strings.
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>> It doesn't, by default, support something called a string.
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That's a CS50 piece of jargon, but very conventional.
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But I can fix this as follows.
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>> If I add one line of code to the top of this program,
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include CS50.h, which is another file somewhere inside of CS50 IDE, somewhere
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on the hard drive, so to speak, of the Ubuntu operating system
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that I'm running, that is the file that's
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going to teach the operating system what a string is, just
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like standard io.h is the file in the operating system that's
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going to teach it what printf is.
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>> Indeed, we would have gotten a very similar message
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if IO had admitted standard IO.h and tried to use printf.
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So I'm going to go ahead and just take Control L to clear my screen.
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Or you can type clear and it will just clear the terminal window.
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But you can still scroll back in time.
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>> And I'm going to rerun Make String.
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Cross my fingers this time, Enter.
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Oh my God, it worked.
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it shows me a long cryptic command that is what Make generated via Clang,
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but no error messages.
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So realize, even though you might get completely
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overwhelmed with the number of error messages,
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it just might be this annoying cascading effect, where Clang doesn't understand
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one thing, which means it then doesn't understand the next word,
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or the next line.
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And so it just chokes on your code.
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But the fix might be simple.
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And so always focus on the very first line of output.
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And if you don't understand it, just look
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for keywords that might be clues, and the line number,
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and the character, where that mistake might be.
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>> Now let me go ahead and type dot slash, string, enter.
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Hm, it's not saying hello anything.
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Why?
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Well, recall, where is it running?
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>> It's probably stuck at the moment in a loop, if you will, on line six,
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because Get String by design, written by CS50 staff,
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is literally meant to just sit there waiting, and waiting,
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and waiting for a string.
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All we mean by string is human input.
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So you know what?
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Let me go ahead.
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And just on a whim, let me type my name, David, enter.
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Now I have a more dynamic program.
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It said, hello David.
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>> If I go ahead and run this again, let me try say Zamila name, enter.
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And now we have a dynamic program.
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I haven't hard coded world.
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I haven't hard coded name, or David, or Zamila.
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>> Now it's much more like the programs we know, where if it take input,
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it produces slightly different output.
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Now, this is not the best user experience, or UX.
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I run the program.
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>> I don't know what I'm supposed to do, unless I actually look at
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or remember the source code.
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So let's make the user experience a little better
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with the simplest of things.
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Let me go back into this program, and simply say printf.
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>> And let me go ahead and say name, colon, and a space, and then a semi-colon.
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And just for kicks, no backlash n.
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And that's deliberate, because I don't want
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the prompt to move to the next line.
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>> I want to, instead, do this, make string to recompile my code into new machine
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