9. If else

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Quick summary of this article

This article explains how to use conditional statements in the Dart programming language to make decisions in code. It covers the basic if, if-else, and else if structures, along with practical examples like calculating grades and comparing numbers.

An if statement runs a block of code only when its condition is true.
An if-else statement provides an alternative block of code to run when the condition is false.
An else if chain allows checking multiple conditions in sequence, with the first true condition's block being executed.
Example programs demonstrate using these statements to assign letter grades based on scores and to compare two user-entered numbers.
The article ends with practice exercises, such as finding the largest of three numbers and calculating discounts based on total purchase amount.

If, Else, Else-If in Dart

In Dart, decision-making is handled using conditional statements like if, else if, else, and the conditional operator ? :. These statements allow your code to execute different blocks based on specified conditions.

1. `if` Statement

The if statement executes a block of code if a specified condition is true:


void main() {
  int number = 10;

  if (number > 0) {
    print('Number is positive');
  }
}

2. `if-else` Statement

The if-else statement executes one block if the condition is true, and another if the condition is false:


void main() {
  int number = -5;

  if (number > 0) {
    print('Number is positive');
  } else {
    print('Number is not positive');
  }
}

3. `else if` Statement

The else if statement allows you to check multiple conditions:


void main() {
  int number = 0;

  if (number > 0) {
    print('Number is positive');
  } else if (number < 0) {
    print('Number is negative');
  } else {
    print('Number is zero');
  }
}

Example: Using Decision-Making to Determine Grade


void main() {
  int score = 85;
  String grade;

  if (score >= 90) {
    grade = 'A';
  } else if (score >= 80) {
    grade = 'B';
  } else if (score >= 70) {
    grade = 'C';
  } else if (score >= 60) {
    grade = 'D';
  } else {
    grade = 'F';
  }

  print('Score: $score, Grade: $grade');
}

Compare Two Numbers


import 'dart:io';

void main() {
  // Ask for the first number
  print('Enter the first number:');
  double? num1 = double.parse(stdin.readLineSync()!);

  // Ask for the second number
  print('Enter the second number:');
  double? num2 = double.parse(stdin.readLineSync()!);

  // Compare the numbers
  if (num1 > num2) {
    print('$num1 is larger than $num2');
  } else if (num2 > num1) {
    print('$num2 is larger than $num1');
  } else {
    print('Both numbers are equal');
  }
}

Exercises

Try solving the following problems using Dart conditional statements:

Enter 3 numbers and find which one is the largest.
Enter marks of 5 subjects, calculate total, percentage, and determine the grade.
Enter prices of 4 articles. Apply discount: if total > 10,000 → 10%, if > 5,000 → 5%, if > 3,000 → 3%, otherwise no discount.
Write a program to print the result (Pass/Fail) based on a student’s marks.

9. If else

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If, Else, Else-If in Dart

1. if Statement

2. if-else Statement

3. else if Statement