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for

The for loop is one of the most common loops in Dart and probably in other programming languages. It allows us to execute a code block repeatedly. In Dart, we have different kinds of for loops:

  • for loop
  • for-in loop

The for loop​

The classic for loop allows us to execute a code block as long as the given condition is true. The syntax is:

for (initialization; condition; statement) {
  // code that will be executed
}
  • initialization: Will be executed only one time. Usually, we will initialize a helper variable that we will use to iterate inside the for loop.
  • condition: The code block inside the for loop will be executed as long as this condition is true.
  • statement: Will be executed every time after the code block. Usually, it is here where we will increase the value of the variable created on the initialization.

Let's write a program to print the numbers from one to ten using a for loop. The flowchart using a for loop is:

The for loop

The for loop

  1. Initialization: we create a variable i with an initial value of 1: var i = 1
  2. Condition: We will loop as long as i is less or equals to 10: i <= 10
  3. We will print the value of i: print( i++ )
  4. Statement: We will increase the value of i by one using ++: i++

Let's run the code in DartPad:

Use a for loop to iterate a list​

We can also use a for loop to iterate each element in a list. Let's write a program to learn how to do it.

Given the next list of cars:

var cars = ['Toyota', 'Mazda', 'Nissan'];

We want to print each of them using a for loop. What do we have to do?

  1. On the initialization, we create a variable with an initial value of 0 because the first position in a list is at the index 0: var i = 0
  2. On the condition, we will check if i is less than the list lenght: i < cars.length, we will loop as long as this condition is true.
  3. On the statement, we will increase the value of i by one: i++.

Let's see the code in DartPad:

The for-in loop​

The for-in loop is used to iterate through elements of collections like the list. It is very common to use the for-in loop when we want to iterate a list and do not want to know the element index.

The syntax is:

for(var item in list) {
  // code that will be executed
}
  • list: Is the list that we want to iterate
  • item: Each item of the list is assigned to this variable

Let's write a program in DartPad to iterate the list of cars from the previous example: