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>> DAVID J. MALAN: Suppose that I'd like
to implement a program that prompts

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the user for a string and then proceeds
to capitalize their input,

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converting any lowercase letters
that they type to uppercase.

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Well, let's go ahead and
implement that program.

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>> Let's first include cs50.h followed
by include stdio.h.

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And so that we can use strlen,
let's include string.h.

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>> Let's next declare main as int main void
and let's now proceed to prompt

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the user for a string.

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Printf, let's prompt them
for some input.

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Now let's declare a string--

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we'll call it s--

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and store in it the result of calling
the cs50 library function GetString.

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>> Let's now proceed to iterate over each
of the characters in s, capitalizing

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any lowercase letters that we see.

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For int, i get 0.

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Let's also declare n as being equal to
the string length of s so that we can

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iterate from i up until n, the
length of s, and on each

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iteration increment i.

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>> And then inside of this loop, let's
first check is the current letter--

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the i-th letter of s, so to speak--

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a lowercase letter.

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If s bracket i is greater than or equal
to lowercase a, and it's less

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than or equal to lowercase z--

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Now if we want to convert a lowercase
letter to uppercase, recall first that

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in ASCII a lowercase a is 97
and an uppercase A is 65.

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Meanwhile, a lowercase b is 98,
and an uppercase B is 66.

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>> If we continue to look at that pattern,
we'll see that the lowercase

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letters are always 32 values higher
than the uppercase letters.

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So if we want to convert from lowercase
to uppercase, it should

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suffice, really, to subtract
32 from the user's input.

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Or more generally, just subtract that
difference between a lowercase a and a

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capital A.

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>> How to express that?

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Well, let's do it in code.

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Printf, quote, unquote "%c" to print
the current character, followed by

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printing whatever's in s bracket i minus
the result of doing lowercase a

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minus uppercase A semicolon.

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In other words, this parenthetical
expression, little a minus big A, is

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going to return to us at
the end of the day 32.

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But I don't have to remember
that it's 32.

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I can allow the computer to figure out
what the difference between lowercase

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a and capital A is.

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>> Meanwhile, once I know that difference,
I can subtract it from s

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bracket i, which will take what's
presumably a lowercase letter to a

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lower value, namely a value that maps
onto an uppercase equivalent.

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Let's now save, compile,
and run this program.

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Make capitalize dot slash capitalized.

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And my input will be hello.

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And there we have, hello.

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>> Now my prompt, admittedly, is
a bit ugly, because we've

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omitted one bit of printing.

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And let's go back and add that.

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At the very bottom of this program,
I'm very simply, and largely for

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aesthetic purpose, going to add printf,
quote, unquote backslash n.

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Let's resave this file,
recompile, rerun.

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>> Make capitalize, dot slash capitalize.

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Again, for input I'll provide "hello"
in all lower case and now hit Enter,

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and "hello," much more cleanly printed.

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