Loops: for and while
on Saturday, 18th of July, 2020
You can repeat expressions in loops using the same keywords as in many languages. There are several kinds of loops in Dart:
- Standard
for
for-in
while
do while
for loops
If you need to know the index, your best bet is the standard for
loop:
for (var i = 0; i < 5; i++) {
print(i);
}
// prints
0
1
2
3
4
If you don't care about the index, the for-in
loop is great option. It's easier to read and more concise to write.
List<String> pets = ['Nora', 'Wallace', 'Phoebe'];
for (var pet in pets) {
print(pet);
}
// prints
'Nora'
'Wallace'
'Phoebe'
while loops
while
loops behave as you'd expect. They evaluate the condition before the loop runs -- meaning it may never run at all:
while(someConditionIsTrue) {
// do some things
}
do-while
loops, on the other hand, evaluate the condition after the loop runs. So they always execute the code in the block at least once:
do {
// do somethings at least once
} while(someConditionIsTrue);
break and continue
These two keywords help you manipulate the flow of the loop. Use continue
in a loop to immediately jump to the next iteration, and use break
to break out of the loop completely:
for (var i = 0; i < 55; i++) {
if (i == 5) {
continue; // jump to next iteration
}
if (i == 10) {
break; // stop loop immediately
}
print(i);
}
// prints to the console
0
1
2
3
4
6
7
8
9
- previous: Control Flow: if, else, else if
- next: Values and variables