Summary: in this tutorial, you’ll learn how to use the Dart if else
statement to do something when a condition is true
and another thing when the condition is false
.
Introduction to the Dart if else statement #
In the previous tutorial, you learned how to do something if a condition is true
by using the if
statement. In practice, you often want to do something if a condition is true
and do another thing if the condition is false
. The Dart if else
statement enables this.
Here’s the syntax of the if else
statement:
if (condition)
{
// statements
}
else
{
// statements
}
Code language: Dart (dart)
In this syntax, the if else
statement evaluates the condition
first.
If the condition
is true
, it’ll then execute the block within the curly braces that follow the if
clause. If the condition is false
, the if else
statement executes the statement in the else
block.
The following flowchart illustrates how the if else
statement works:
Dart if else statement examples #
Let’s take some examples of using the if else
statement to understand how it works.
1) Simple Dart if else statement examples #
The following example uses the if else
statement to show a message based on the value of the isWeekend
variable:
void main() {
bool isWeekend = true;
if (isWeekend) {
print("Let's play!");
} else {
print("Let's go to work!");
}
}
Code language: Dart (dart)
Output:
Let's play!
Code language: Dart (dart)
In this example, the isWekeend
is true
. Therefore, the program displays the message "Let's play!"
.
In the following, we change the value of the isWeekend
variable to false
:
void main() {
bool isWeekend = false;
if (isWeekend) {
print("Let's play!");
} else {
print("Let's go to work!");
}
}
Code language: Dart (dart)
Output:
Let's go to work!
Code language: Dart (dart)
Since the expression isWeekend
is false
, the else
block executes. Therefore, the program shows the message "Let's go to work!"
.
2) Using Dart if else statement with a complex condition example #
The following example uses the if else
statement with a complex condition:
void main() {
bool isWeekend = true;
String weather = "sunny";
if (isWeekend && weather == "sunny") {
print("Let's go to the beach!");
} else {
print("Let's go to work!");
}
}
Code language: Dart (dart)
Output:
Let's go outside.
Code language: Dart (dart)
In this example, we set the isWeekend
to true
and weather
to sunny
. Therefore, the following expression evaluates to true
:
isWeekend && weather == "sunny"
Code language: Dart (dart)
Hence, the if
block executes that shows the message "Let's go to the beach!"
.
In the following example, we change the isWeekend
to false
:
void main() {
bool isWeekend = false;
String weather = "sunny";
if (isWeekend && weather == "sunny") {
print("Let's go to the beach!");
} else {
print("Let's go to work!");
}
}
Code language: Dart (dart)
Output:
Let's go to work!
Code language: Dart (dart)
Because the following expression evaluates to false
, the else
clause executes that displays the message "Let's go to work!"
:
isWeekend && weather == "sunny"
Code language: JavaScript (javascript)
Summary #
- Use Dart
if else
statement to do something if a condition istrue
and do another thing if the condition isfalse
.