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1.1.1 Defining a variable
The following five Yorick statements define the five variables c,
m, E, theta, and file:
 c = 3.00e10; m = 9.11e28
E = m*c^2
theta = span(0, 6*pi, 200)
file = create("damped.txt")

Variable names are case sensitive, so E is not the same variable
as e. A variable name must begin with a letter of the alphabet
(either upper or lower case) or with an underscore (_);
subsequent characters may additionally include digits.
A semicolon terminates a Yorick statement, so the first line contains
two statements. To make Yorick statements easier to type, you don't
need to put a semicolon at the end of most lines. However, if you are
composing a Yorick program in a text file (as opposed to typing
directly to Yorick itself, a semicolon at the end of every line
reduces the chances of a misinterpretation, and makes your program
easier to read.
Conversely, a new line need not represent the end of a statement. If
the line is incomplete, the statement automatically continues on the
following line. Hence, the second and third lines above could have
been typed as:
 E=
m *
c^2
theta= span(0, 6*pi,
200)

In the second line, * and ^ represent multiplication and
raising to a power. The other common arithmetic operators are
+, , / (division), and % (remainder or
modulo). The rules for forming arithmetic expressions with these
operators and parentheses are the same in Yorick as in Fortran or C
(but note that ^ does not mean raise to a power in C, and
Fortran uses the symbol ** for that operation).
The span function returns 200 equally spaced values beginning
with 0 and ending with 6*pi. The variable pi is
predefined as 3.14159...
The create function returns an object representing the new file.
The variable file specifies where output functions should write
their data. Besides numbers like c, m, and E, or
arrays of numbers like theta, or files like file, Yorick
variables may represent several other sorts of objects, taken up in
later chapters.
The = operator is itself a binary operator, which has the side
effect of redefining its left operand. It associates from right to
left, that is, the rightmost = operation is performed first (all
other binary operators except ^ associate from left to right).
Hence, several variables may be set to a single value with a single
statement:
 psi = phi = theta = span(0, 6*pi, 200)

When you define a variable, Yorick forgets any previous value and data
type:
