Dart if else if

Summary: in this tutorial, you’ll learn how to use the Dart if else if statement to check multiple conditions and do something if a condition is true.

Introduction to the Dart if else if statement

The if statement checks a condition only does something if the condition is true.

The if else statement checks one condition and does something if a condition is true or another thing if the condition is false.

Therefore, both the if and if else statements allow you to do something based on the result of one condition.

To do something based on the result of multiple conditions, you use the if else if statement.

The following shows the syntax of the if else if statement:

if (condition1)
{
    // statement 1
}
else if (condition2)
{
    // statement 2
}
else if (condition3)
{
    // statement 3
}
else 
{
    // else statment
}Code language: Dart (dart)

In this syntax:

• The if else if statement may have multiple else if clause where each clause checks a condition.
• The if else if statement checks the condition1, condition2, … from top to bottom sequentially. If a condition is true, it executes the corresponding block that follows the condition. The statement will stop evaluating the remaining conditions as soon as a condition is true.
• If no condition is true, the statement in the else clause executes. The else clause is optional. It means that if you omit the else clause and no condition is true, the if else if statement doesn’t do anything.

The following flowchart illustrates how the if else if statement works:

Dart if else if examples

The following examples illustrate how to use the if else if statement.

1) Simple Dart if else if statement example

The following example shows how to use the if else if statement to display the day name based on a day number entered by users:

void main() {

  String season = "";
  String month = "Feb";

  if (month == "Jan" || month == "Feb" || month == "March") {
    season = "Spring";
  } else if (month == "Apr" || month == "Jun" || month == "July") {
    season = "Summer";
  } else if (month == "Aug" || month == "Sep" || month == "Oct") {
    season = "Autumn";
  } else if (month == "Nov" || month == "Dec" || month == "Jan") {
    season = "Winter";
  } else {
    season = "Invalid";
  }

  print(season);
}Code language: Dart (dart)

Output:

SpringCode language: plaintext (plaintext)

How it works.

• First, declare the season and month variables and initialize their values to "" and "Feb".
• Second, use the if else if statement to assign a value to the season variable based on the value of the month.

2) Using the Dart if else if statement to develop a body mass index calculation program

The body mass index (BMI) is a person’s weight in kilograms divided by the square of height in meters. The BMI classifies a person’s weight category as underweight, healthy weight, overweight, and obesity.

The following program calculates the body mass index (BMI):

void main() {
  double weight = 80;
  double height = 1.9;
  double bmi = weight / (height * height);

  String status = "";

  if (bmi < 18.5) {
    status = "Underweight";
  } else if (bmi >= 18.5 && bmi <= 24.9) {
    status = "Healthy Weight";
  } else if (bmi >= 25 && bmi <= 29.9) {
    status = "Overweight";
  } else {
    status = "Obesity";
  }

  print("BMI $bmi: Status: $status");
}Code language: Dart (dart)

How it works.

First, declare the height and weight variables and assign the values:

double weight = 80;
double height = 1.9;Code language: Dart (dart)

Second, calculate the BMI number:

double bmi = weight / (height * height);

Third, assign the status based on BMI:

String status = "";

if (bmi < 18.5) {
  status = "Underweight";
} else if (bmi >= 18.5 && bmi <= 24.9) {
  status = "Healthy Weight";
} else if (bmi >= 25 && bmi <= 29.9) {
  status = "Overweight";
} else {
  status = "Obesity";
}Code language: Dart (dart)

Finally, show the BMI result and the status:

print("BMI $bmi: Status: $status");Code language: Dart (dart)

Summary

• Use the Dart if else if statement to check multiple conditions and do something if a condition is true.