Loops

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Published May 18, 2024
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In Dart, Loops are used to iterate over iterables such as lists, maps, etc., allowing operations to be performed repeatedly. Dart supports the following types of loops:

for Loop

The for loop is utilized when the number of iterations for a code block is predetermined. It shares similarities with the for loop syntax in languages such as C, C++, Java, etc.

Syntax

for(initialization; condition; increment/decrement){
  //Body of the loop
}

Example

void main()
{
for (int n = 0; n <= 5; n++) {
print(n);
}
}

The above code produces the following output:

0
1
2
3
4
5

for-in Loop

The for-in loop is slightly different from the for loop. It iterates over each element of a Dart object or expression, one at a time. It’s preferred when there’s no need for counter iteration.

Syntax

for (var in expression) {
   // Body of the loop
}

Example

void main()
{
var nums = [ 1, 2, 3, 4, 5 ];
for (int n in nums) {
print(n);
}
}

The above code gives the following output:

1
2
3
4
5

forEach Loop

The forEach loop iterates over all elements in a container or collection and invokes a specified function for each element.

Syntax

collection.forEach(void f(value))

f(value) is a parameter which is used to call the function f for each value in the collection.

Example

void main()
{
var nums = [1,2,3,4,5];
nums.forEach((var n)=> print(n));
}

The above code gives the following output:

1
2
3
4
5

while Loop

The while loop executes a block of code until the given condition is false. It is more beneficial when the number of executions is not known.

Syntax

while(condition) {
   // loop body
}

Example

void main()
{
var n = 4;
int i = 1;
while (i <= n) {
print('Hello there');
i++;
}
}

The output of the above code is:

Hello there
Hello there
Hello there
Hello there

do-while Loop

The do-while loop is similar to the while loop, with the key difference being that it executes the loop statement before checking the given condition. Therefore, the block of code inside the loop is guaranteed to execute at least once.

Syntax

do {
    // loop body
} while(condition);

Example

void main()
{
var n = 4;
int i = 1;
do {
print('Hello there');
i++;
} while (i <= n);
}

The output of the above code is:

Hello there
Hello there
Hello there
Hello there

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