Strings and Char

What you’ll build

A program that reports on a line of text: it tidies the line, counts its words, puts it in title case, and lays out a small table. A String is text, and a Char is one character of it.

Putting values in strings

Braces in a string hold any expression, whose value is put in its place. + joins two strings. A backslash starts an escape, like \" for a quote or \n for a line break, and {{ and }} are literal braces.

Import std.core

Local name = "fox"
Local legs = 4
Print("The {name} has {legs} legs, {legs * 2} with a friend.")
Print("Say \"hi\"" + " to the " + name + ".")
Print("Braces: {{like this}}")

The fox has 4 legs, 8 with a friend.
Say "hi" to the fox.
Braces: {like this}

+ only joins a String to a String; anything else goes in braces.

Format specs

After a colon inside the braces, a format spec says how to write the value: <, >, or ^ and a width pad it on the right, left, or both sides; .2 gives two digits after the point; , groups digits in thousands; and % writes a fraction as a percentage.

Import std.core

Local items = ["apples", "pears", "figs"]
Local prices = [1.5, 12.25, 120.0]
For i, item In items
    Print("{item:<8}|{prices[i]:>8.2}|")
End For
Print("{1234567:,} {0.075:.1%} {7:03}")

apples  |    1.50|
pears   |   12.25|
figs    |  120.00|
1,234,567 7.5% 007

For i, item In items gives each element with its index.

String’s Methods

A String’s Methods, the functions called on a String with a dot, come from std.text, so a file that uses them imports it. Trim takes off the spaces at both ends, Split cuts the text at a separator, and Find gives the position of some text, or Null when it isn’t there. A String never changes: a Method that changes text, like Trim or Replace, gives a new String.

Import std.core
Import std.text

Local line = "  the QUICK brown fox jumps over the lazy dog  "
Local text = line.Trim()
Local words = text.Split(" ")
Print("\"{text}\"")
Print("{words.Count} words; the third is \"{words[2]}\", {words[2].Length} letters")
Print(text.ToLower())
Print("fox at {text.Find("fox") ?? -1}, cat at {text.Find("cat") ?? -1}")
Print(text.Replace("lazy", "sleepy"))

"the QUICK brown fox jumps over the lazy dog"
9 words; the third is "brown", 5 letters
the quick brown fox jumps over the lazy dog
fox at 16, cat at -1
the QUICK brown fox jumps over the sleepy dog

?? -1 gives -1 when Find gives Null. Nullable types explains ??.

Characters

A Char is one Unicode character, written in single quotes, like 'a'. A string’s Chars is an array of its characters, and a Char has Methods such as IsLetter and ToUpper. A StringBuilder builds a string a piece at a time.

Import std.core
Import std.text

Function TitleCase(text: String): String
    Local out = StringBuilder()
    Local start = True
    For c In text.Chars
        If c.IsLetter()
            out.Append(start ? c.ToUpper() : c.ToLower())
            start = False
        Else
            out.Append(c)
            start = True
        End If
    End For
    Return out.ToString()
End Function

Print(TitleCase("the QUICK brown fox"))
Print("naïve".Length, "naïve".CharCount)

The Quick Brown Fox
6 5

A String is stored as UTF-8, and its Length counts bytes: ï takes two, so “naïve” has a Length of 6 and a CharCount of 5. Positions, like what Find gives, are byte positions too. There’s no text[i], since finding the i-th character means reading from the start; go through Chars instead.

Raw and multi-line strings

A raw string, r"...", has no escapes or interpolation, which suits paths and patterns. Three quotes start a string of several lines. The closing quotes’ indentation is taken off every line, so the string can be indented with the code around it.

Import std.core

Local folder = r"C:\reports\new"
Local animal = "fox"
Local note = """
    Report on the {animal}:
      - quick
      - brown
    """
Print(folder)
Print(note)

C:\reports\new
Report on the fox:
  - quick
  - brown

What you learned

• "{expr}" puts a value in a string, and a format spec after a colon lays it out.
• + joins Strings only; everything else goes in braces.
• String’s Methods come from std.text, and the ones that change text give a new String, since a String never changes.
• A Char is one character; Chars gives a String’s characters, and Length counts its bytes.
• r"..." is a raw string, and """ starts one of several lines.