Editing Side effect (computer science) (section)

== Example ==
One common demonstration of side effect behavior is that of the [[assignment operator]] in [[C (programming language)|C]]. The assignment <code>a = b</code> is an expression that evaluates to the same value as the expression <code>b</code>, with the side effect of storing the [[value (computer science)#lrvalue|R-value]] of <code>b</code> into the [[value (computer science)#lrvalue|L-value]] of <code>a</code>. This allows multiple assignment:

<syntaxhighlight lang="c">
a = (b = 3);  // b = 3 evaluates to 3, which then gets assigned to a
</syntaxhighlight>

Because the operator [[operator associativity#Right-associativity of assignment operators|right associates]], this is equivalent to

<syntaxhighlight lang="c">
a = b = 3;
</syntaxhighlight>

This presents a potential hangup for novice programmers who may confuse

<syntaxhighlight lang="c">
while (b == 3) {}  // tests if b evaluates to 3
</syntaxhighlight>

with

<syntaxhighlight lang="c">
while (b = 3) {}  // b = 3 evaluates to 3, which then casts to true so the loop is infinite
</syntaxhighlight>