do-while:
do
{
i++;
++j;
System.out.println( i * j );
}
while ((i < 10) && (j*j != 25));
I am learning about do-while vs while at the moment and would like to rewrite the above java fragment (already declared and initialized) using a while instead. Are the below rewritten codes correct way to do so:
while:
while ((i < 10) && (j*j != 25))
{
i++;
++j;
System.out.println( i * j );
}
Cheers
The difference between a do-while
and a while
is when the comparison is done. With a do-while
, you'll compare at the end and hence do at least one iteration.
do
{
i++;
++j;
System.out.println( i * j );
}
while ((i < 10) && (j*j != 25));
is equivalent to:
i++;
++j;
System.out.println( i * j );
while ((i < 10) && (j*j != 25)) {
i++;
++j;
System.out.println( i * j );
}
A do-while
loop is an exit controlled loop which means that it exits at the end. A while
loop is an entry controlled loop which means that the condition is tested at the beginning and as a consequence, the code inside the loop might not even be executed.
do {
<block>
} while (<condition>);
is equivalent to:
<block>
while (<condition>) {
<block>
};
A typical use case for a do-while
is the following: you ask the user something and you want do repeat the operation while the input is not correct.
do {
// Ask something
} while (input is not correct);
In that case, you want to ask at least once and it's usually more elegant than using a while
which would require either to duplicate code, or to add an extra condition or setting an arbitrary value to force entering the loop the first time.
At the opposite, while
loops are much more commons and can easily replace a do-while
(not all languages have both loops).