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Conditional Statements Implementing Control-Flow Logic in C# SoftUni Team Technical Trainers Software University http://softuni.bg
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2 1.Comparison and Logical Operators 2.The if Statement 3.The if-else Statement 4.Nested if Statements 5.The switch-case Statement Table of Contents
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Comparison and Logical Operators
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4 Operator Notation in C# Applicable for Equals== strings / numbers / dates / most objects Not Equals != Greater Than > numbers / dates / comparable objects Greater Than or Equals >= Less Than < Less Than or Equals <= Comparison Operators bool result = (5 <= 6); Console.WriteLine(result); // True Example:
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5 De Morgan laws !!A A !(A || B) !A && !B !(A && B) !A || !B Logical OperatorsOperator Notation in C# Example Logical NOT ! !false true Logical AND && true && true true Logical OR || true || false true Logical Exclusive OR (XOR) ^ true ^ false true
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if and if-else Implementing Conditional Logic
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7 The simplest conditional statement Enables you to test for a condition Branch to different blocks in the code depending on the result The simplest form of the if statement: The if Statement if (condition) { statements; statements;}
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8 The condition can be: Boolean variable Boolean logical expression Comparison expression The condition cannot be integer variable (like in C / C++) The statement can be: Single statement ending with a semicolon Block enclosed in curly braces Condition and Statement
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9 The condition is evaluated If it is true, the statement is executed If it is false, the statement is skipped How It Works? true condition statements false
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10 The if Statement – Example static void Main() { Console.WriteLine("Enter two numbers."); Console.WriteLine("Enter two numbers."); int biggerNum = int.Parse(Console.ReadLine()); int biggerNum = int.Parse(Console.ReadLine()); int smallerNum = int.Parse(Console.ReadLine()); int smallerNum = int.Parse(Console.ReadLine()); if (smallerNum > biggerNum) if (smallerNum > biggerNum) { biggerNum = smallerNum; biggerNum = smallerNum; } Console.WriteLine("The greater number is: {0}", biggerNum); Console.WriteLine("The greater number is: {0}", biggerNum);}
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The if Statement Live Demo
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12 More complex and useful conditional statement Executes one branch if the condition is true, and another if it is false The simplest form of an if-else statement: The if-else Statement if (expression) { some_statement; some_statement;}else{ another_statement; another_statement;}
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13 The condition is evaluated If it is true, the first statement is executed If it is false, the second statement is executed How It Works? condition firststatement true secondstatement false
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14 Checking a number if it is odd or even if-else Statement – Example string s = Console.ReadLine(); int number = int.Parse(s); if (number % 2 == 0) { Console.WriteLine("This number is even."); Console.WriteLine("This number is even.");}else{ Console.WriteLine("This number is odd."); Console.WriteLine("This number is odd.");}
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The if-else Statement Live Demo
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Nested if Statements Creating More Complex Logic
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17 if and if-else statements can be nested Used inside one inside another Each else corresponds to its closest preceding if Nested if Statements if (expression) { if (expression) if (expression) some_statement; some_statement; else else another_statement; another_statement;}else third_statement; third_statement;
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18 Always use { … } blocks to avoid ambiguity Even when a single statement follows Avoid using more than three levels of nested if statements Put the case you normally expect to process first Then write the unusual cases Arrange the code to make it more readable Nested if – Good Practices
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19 Nested if Statements – Example if (first == second) { Console.WriteLine("These two numbers are equal."); Console.WriteLine("These two numbers are equal.");}else{ if (first > second) if (first > second) { Console.WriteLine("The first number is bigger."); Console.WriteLine("The first number is bigger."); } else else { Console.WriteLine("The second is bigger."); Console.WriteLine("The second is bigger."); }}
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Nested if Statements Live Demo
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21 We may need to use another if -construction in the else block Thus else if can be used: Multiple if-else-if-else-… int ch = 'X'; if (ch == 'A' || ch == 'a') { Console.WriteLine("Vowel [ei]"); Console.WriteLine("Vowel [ei]");} else if (ch == 'E' || ch == 'e') { Console.WriteLine("Vowel [i:]"); Console.WriteLine("Vowel [i:]");} else if … else …
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Multiple if-else Statements Live Demo
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switch-case Performing Several Comparisons at Once
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24 Selects for execution a statement from a list depending on the value of the switch expression The switch-case Statement switch (day) { case 1: Console.WriteLine("Monday"); break; case 1: Console.WriteLine("Monday"); break; case 2: Console.WriteLine("Tuesday"); break; case 2: Console.WriteLine("Tuesday"); break; case 3: Console.WriteLine("Wednesday"); break; case 3: Console.WriteLine("Wednesday"); break; case 4: Console.WriteLine("Thursday"); break; case 4: Console.WriteLine("Thursday"); break; case 5: Console.WriteLine("Friday"); break; case 5: Console.WriteLine("Friday"); break; case 6: Console.WriteLine("Saturday"); break; case 6: Console.WriteLine("Saturday"); break; case 7: Console.WriteLine("Sunday"); break; case 7: Console.WriteLine("Sunday"); break; default: Console.WriteLine("Error!"); break; default: Console.WriteLine("Error!"); break;}
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25 1.The expression is evaluated 2.When one of the constants specified in a case label is equal to the expression The statement that corresponds to that case is executed 3.If no case is equal to the expression If there is default case, it is executed Otherwise the control is transferred to the end point of the switch statement How switch-case Works?
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The switch-case Statement Live Demo
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27 Variable types like string, enum and integral types can be used for switch expression The value null is permitted as a case label constant The keyword break exits the switch statement "No fall through" rule You are obligated to use break after each case Multiple labels that correspond to the same statement are permitted Using switch : Rules
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28 Multiple labels allow matching several cases and executing the same statement in more than one case Multiple Labels – Example switch (animal) { case "dog": case "dog": Console.WriteLine("MAMMAL"); Console.WriteLine("MAMMAL"); break; break; case "crocodile": case "crocodile": case "tortoise": case "tortoise": case "snake": case "snake": Console.WriteLine("REPTILE"); Console.WriteLine("REPTILE"); break; break; default: default: Console.WriteLine("I don't know such animal!"); Console.WriteLine("I don't know such animal!"); break; break;}
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Multiple Labels in a switch-case Live Demo
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30 There must be a separate case for every normal situation Put the normal case first Put the most frequently executed cases first and the least frequently executed last Order cases alphabetically or numerically In default use case that cannot be reached under normal circumstances Using switch – Good Practices
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31 Comparison and logical operators are used to compose logical conditions The conditional statements if and if-else conditionally execution of blocks of code Constantly used in computer programming Conditional statements can be nested The switch statement easily and elegantly checks an expression for a sequence of values Summary
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? ? ? ? ? ? ? ? ? Conditional Statements https://softuni.bg/courses/programming-basics/
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Homework Review Live Demo
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License This course (slides, examples, demos, videos, homework, etc.) is licensed under the "Creative Commons Attribution- NonCommercial-ShareAlike 4.0 International" licenseCreative Commons Attribution- NonCommercial-ShareAlike 4.0 International 34 Attribution: this work may contain portions from "Fundamentals of Computer Programming with C#" book by Svetlin Nakov & Co. under CC-BY-SA licenseFundamentals of Computer Programming with C#CC-BY-SA "C# Part I" course by Telerik Academy under CC-BY-NC-SA licenseC# Part ICC-BY-NC-SA
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