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  1.2.5.1 extern statements 
Suppose you want to write a function which sets the value of the
theta array used by all the variants of the q_out
function: 
 |  | func q_out_domain(start, stop, n)
{
  extern theta;
  theta = span(start, stop, n);
}
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Without the extern statement, theta will be a local
variable, whose external value is restored when q_out_domain
returns (thus, the function would be a no-op).  With the extern
statement, q_out_domain has the intended side effect of setting
the value of theta.  The new theta would be used by
subsequent calls to q_out. 
Any number of variables may appear in a single extern statement:
 
 |  | extern var1, var2, var3, var4;
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