ASCII values

Every character in a printed string (“B”,”p”,”ñ”, etc.) has its own number called an “ASCII value.”

In Hugo, if we want to alphabetize some strings or change the case of something or even ROT13 something, we would do it by going through the string, character by character, changing or noting the ASCII values as necessary.

Alphabetization

The hugolib.h routine StringCompare compares each digit of two strings. If the first digit of the first word is lexically lower, StringCompare would return -1 at this point. Looking at the chart, we can see that it means that word would be alphabetized first. Conversely, if that digit was lexically higher, we’d know that the second word would come first, alphabetically (and StringCompare would return 1). If both of those digits are equal, we know that it is the same letter. StringCompare then goes on to compare the second character of both strings (and so on). If it gets to the end of both strings without finding a difference, StringCompare returns 0 and we know the strings are identical.

Uppercase/lowercase modification

Here is a bit of code from the make-the-string-lowercase routine on the String Manipulation page:

if array stringarray[i] >= 'A' and array stringarray[i] <= 'Z'
    array stringarray[i] = array stringarray[i] + ('a'-'A')

That code basically says, “if this letter has a value between 65 and 90 (the uppercase range), make it equal the same number plus 32 (the difference between “a” (97) and “A” (65)). That should be the lowercase version of that letter.”

In any case, knowing about ASCII values (and having a chart to reference like the one above) will make string-modification routines a lot easier to read (and write!).