**simple tests:

input is x
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
x 

That's all, folks!

input is ( x + y )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
x y + 

That's all, folks!

input is ( xy Q zw )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
xy zw Q 

That's all, folks!

input is ( x + 
    z )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
x z + 

That's all, folks!

**more complicated tests:

input is ( ( x + y ) / z )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
x y + z / 

That's all, folks!

input is ( a + ( b / c ) )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
a b c / + 

That's all, folks!

input is ( ( a + b ) * ( c / d ) )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
a b + c d / * 

That's all, folks!

input is ( ( ( ( a + b ) * ( c * d ) ) - ( e - f ) ) Z 	( ( k Q l ) + ( ( g / h ) / ( i % j ) ) ) )
Enter the expression to evaluate (multiple lines okay, control-D to end):

In postfix notation:
a b + c d * * e f - - k l Q g h / i j % / + Z 

That's all, folks!