Jtdylktuy

newcommand*{name}[1][C]{%

I have come very familiar with newcommand however, I came across this line of code and i do not know what the [C] is for.

LaTeX's newcommand has the following syntax:

newcommand *{<FOO>}[<i>]{<TEXT>}

User command to define FOO to be a macro with i arguments (i = 0 if missing)
having the definition <TEXT>. Produces an error if FOO already defined.
Normally the command is defined to be long (i.e. it may take multiple paragraphs in its argument). In the star-form, the command is not defined as long
and a blank line in any argument to the command would generate an error.

If you define a command with at least one argument (i > 0), you can specify an additional (optional) argument before the definition <TEXT>. This optional argument will be used as the "default" value for a first optional argument to FOO.

So, as an example, consider

newcommand{FOO}[2]{<TEXT>}

This command has two mandatory arguments and is therefore used as FOO{<one>}{<two>}. However,

newcommand{FOO}[2][X]{<TEXT>}

takes two (2) arguments, the first of which is optional and has a default of X (if not supplied). You can use it as FOO{<one>} (which is equivalent to FOO[X]{<one>}) or FOO[<one>]{<two>}. Similarly,

newcommand{FOO}[1][X]{<TEXT>}

takes a single (1) optional argument that has a default value of X (if not supplied) and can be used as FOO (which is equivalent to FOO[X]) or FOO[<one>].

In your particular case,

newcommand*{name}[1][C]{<TEXT>}

defines name to (be non-long; that is, <TEXT> cannot have blank lines and) take a single (1) optional argument that defaults to C if not supplied. You can use it as name (which is equivalent to name[C]) or name[<one>].

Reference:

• LaTeX2e sources




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