update r3_assignment

Assignment statement

An assignment statement assigns the value of an expression to a simple variable, or to a subscript or slice of a variable. e.g.

x = a + b 
y[i] = y[i] + 1 
y[i..j] = {1, 2, 3} 

The previous value of the variable, or element(s) of the subscripted or sliced variable are discarded. For example, suppose x was a 1000-element sequence that we had initialized with:

object x 
x = repeat(0, 1000)  -- a sequence of 1000 zeros 

and then later we assigned an atom to x with:

x = 7 

This is perfectly legal since x is declared as an object. The previous value of x, namely the 1000-element sequence, would simply disappear. Actually, the space consumed by the 1000-element sequence will be automatically recycled due to Euphoria's dynamic storage allocation.

Note that the equals symbol '=' is used for both assignment and for equality testing. There is never any confusion because an assignment in Euphoria is a statement only, it can't be used as an expression (as in C).

Assignment with Operator

Euphoria also provides some additional forms of the assignment statement.

To save typing, and to make your code a bit neater, you can combine assignment with one of the operators:

+ - / * & 

For example, instead of saying:

mylongvarname = mylongvarname + 1 

You can say:

mylongvarname += 1 

Instead of saying:

galaxy[q_row][q_col][q_size] = galaxy[q_row][q_col][q_size] * 10 

You can say:

galaxy[q_row][q_col][q_size] *= 10 

and instead of saying:

accounts[start..finish] = accounts[start..finish] / 10 

You can say:

accounts[start..finish] /= 10 

In general, whenever you have an assignment of the form:

left-hand-side = left-hand-side op expression 

You can say:

left-hand-side op= expression 

where op is one of:

+ - * / & 

When the left-hand-side contains multiple subscripts/slices, the op= form will usually execute faster than the longer form. When you get used to it, you may find the op= form to be slightly more readable than the long form, since you don't have to visually compare the left-hand-side against the copy of itself on the right side.

You cannot use assignment with operators while declaring a variable, because that variable is not initialized when you perform the assignment.

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