# Variables, Conditionals and Exercises #### Java 101 - Class 1 What we want to achieve * Exercises * Debugging * תנאי מקוצר - *ternary* conditional *operator* * MyConsole and Scanner * *compilation* and *runtime errors* * compiling and running via cmd/terminal * טבלת מעקב (מצגות) What we learnt in class * חשבון ומודלו * if and if-else * printing to screen `System.out.println` * while * Interger.MAX\_VALUE * המרת מספרים מממשי לבינראי ולהיפך ## Exercises ### I0 - קלט ופלט **פלט** נעשה ע"י הפקודה ```java System.out.println("hello 👋") ``` ברוב הide נוכל לכתוב `syso` או `sout` כדי שהide ישלים אותנו אוטומטית בקלט יש לנו 2 דרכים * Scanner * MyConsole (מה שלמדים בהתחלה בשיעור) #### MyConsole ```java public class Main { public static void main(String[] args) { int myInt = MyConsole.readInt("enter int: "); double myDouble = MyConsole.readDouble("enter double: "); String myString = MyConsole.readString("enter word: "); System.out.println("\nint is: " + myInt); System.out.println("double is: " + myDouble); } } ``` ``` enter int: 4.5 Not an integer. Please try again! enter int: 7 enter double: 10.51 int is: 7 double is: 10.51 string is: hello ``` #### Scanner ```java Scanner scanner = new Scanner(System.in); String myString = scanner.next(); int myInt = scanner.nextInt(); scanner.close(); System.out.println("myString is: " + myString); System.out.println("myInt is: " + myInt); ``` input: ``` Hi 5 ``` output: ``` myString is: Hi myInt is: 5 ``` #### Variables משתנים פרימיטיבים ![](https://vertex-academy.com/tutorials/wp-content/uploads/2016/08/800x459xvariables-Java-vertex-academy.png.pagespeed.ic.CKRV4A1dpK.webp) [Image Source](https://vertex-academy.com/tutorials/en/types-variables-java-create-variable/) ```java public class Main { public static void main(String[] args) { byte tinyNum = 100; short smallNum = 20_000; int num = 1<<20; long largeNum = (long) 1<<50; float decimal = 10.5050f; double largeDecimal = 3.141592653589; boolean trueOrFalse = true; System.out.println(num); System.out.println(largeNum); System.out.println(decimal); if (trueOrFalse) System.out.println("true"); else System.out.println("false"); } } ``` ``` 1048576 1125899906842624 10.505 true ``` #### if and if else ![Wikipedia if-else flow chart](https://s3.amazonaws.com/hr-challenge-images/13689/1446563087-4ec019a919-332px-If-Then-Else-diagram.svg.png) #### תרגיל: תנאים Given an integer *n* , perform the following conditional actions: * If *n* is odd, print `Strange` * If *n* is even and in the inclusive range of 2 to 5 , print `Not Strange` * If *n* is even and in the inclusive range of 6 to 20, print `Strange` * If *n* is even and greater than 20, print `Not Strange` **Solution** ```java import java.util.Scanner; public class Main { public static void main(String[] args) { System.out.print("Enter an integer: "); Scanner scanner = new Scanner(System.in); int n = scanner.nextInt(); if (n%2==1) System.out.println("Strange"); else if (n%2==0 && n>=2 && n<=5) System.out.println("Not Strange"); else if (n%2==0 && n>=6 && n<=20) System.out.println("Strange"); else if (n%2==0 && n>20) System.out.println("Not Strange"); } } ``` ``` Enter an integer: 20 Strange ``` #### תרגיל: האם זה שנה מעוברת כתבו תוכנית המחזיר האם השנה הוא שנה מעוברת או לא To determine whether a year is a leap year, follow these steps: 1. If the year is evenly divisible by **4**, go to step 2. Otherwise, go to step 5. 2. If the year is evenly divisible by **100**, go to step 3. Otherwise, go to step 4. 3. If the year is evenly divisible by **400**, go to step 4. Otherwise, go to step 5. 4. The year is a leap year (it has 366 days). 5. The year is not a leap year (it has 365 days). examples: * 1600 ✔️ leap year * 1700 ❌ not leap year * 1800 ❌ not leap year * 1900 ❌ not leap year * 2000 ✔️ leap year * 2001 ❌ not leap year * 2004 ✔️ leap year ```java package com.company; import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("enter year: "); int year = sc.nextInt(); boolean four = ((year % 4) == 0); boolean hundred = ((year % 100) == 0); boolean fourhundred = ((year % 400) == 0); boolean isleapyear = fourhundred || (four && !hundred); System.out.println(year + " is a leap year? " + isleapyear); sc.close(); } } ``` ``` enter year: 2021 2021 is a leap year? false ``` בא עכשיו לגרום לתוכנית לא להפסק ```java package com.company; import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int year=-1; while (year!=0) { System.out.print("enter year: "); year = sc.nextInt(); boolean four = ((year % 4) == 0); boolean hundred = ((year % 100) == 0); boolean fourhundred = ((year % 400) == 0); boolean isleapyear = fourhundred || (four && !hundred); System.out.println(year + " is a leap year? " + isleapyear); } sc.close(); } } ``` ``` enter year: 2020 2020 is a leap year? true enter year: 2021 2021 is a leap year? false enter year: 0 0 is a leap year? true ``` כמו שניתן לשים לב, עטפנו את התוכנית שלנו עם `while` ```java while (year!=0) { ... } ``` > שים לב שמנו את Scanner בחוץ ככה לא נצטרך פעם לייצר משתנה חדש כל פעם. בנוסף גם הסגירה שלו בחוץ **תרגילים: המרות** מה יהיה הפלט? ```java public class Main { public static void main(String[] args) { int x = 8, y = 13; double d = y/x; System.out.println("y/x = "+d); d = (double)y/x; System.out.println("y/x = "+d); double a = 5, b = 18; int c = (int)(a/b); System.out.println("a/b = "+c); } } ``` ``` y/x = 1.0 y/x = 1.625 a/b = 0 ``` שאלו את עצמכם למה ההדפסה הראשונה יוצא 1.0 🤔 **מה יהיה הפלט?** ```java public class Main { public static void main(String[] args) { double num = 123.45687; System.out.println((int)(num * 100) / 100.0); } } ``` ``` 123.45 ``` **מה יהיה הפלט?** ```java public class Main { public static void main(String[] args) { float x = (float)1.0, y = 3.0f, z=99; System.out.println(x/y); System.out.println(z); } } ``` ``` 0.33333334 99.0 ``` כאן הכזרנו על 3 משתני float לולי היינו עושים ככה הקוד לא מתקפל ```java float x = (float)1.0, y = 3.0, z=99; ``` לא היה מתקפל כי ה y היה double. לזה קוראים ***compilation error*** ### Runtime Error ```java public class Main { public static void main(String[] args) { System.out.println("Integer.MAX_VALUE = "+Integer.MAX_VALUE); System.out.println("Integer.MIN_VALUE = "+Integer.MIN_VALUE); System.out.println("Integer.SIZE = "+Integer.SIZE); int x = Integer.MAX_VALUE + 1; System.out.println("Integer.MAX_VALUE + 1 = "+x); int a = 0, b=10, z; z = b/a; System.out.println("b/a = "+z); } } ``` ``` Integer.MAX_VALUE = 2147483647 Integer.MIN_VALUE = -2147483648 Integer.SIZE = 32 Integer.MAX_VALUE + 1 = -2147483648 Exception in thread "main" java.lang.ArithmeticException: / by zero at com.company.Main.main(Main.java:11) ``` > מאוחר יותר נלמד על try וcatch שיעזרו לנו להתמודד עם שגיאות #### תרגיל כתבו אם מספר הוא int, short or long ![](https://www.codingeek.com/wp-content/uploads/2017/07/Integer-Sizes.png) ```java import java.util.Scanner; public class Main { public static void main(String[] args) { System.out.print("Enter an integer: "); Scanner scanner = new Scanner(System.in); int n = scanner.nextInt(); if (Short.MAX_VALUE>=n && Short.MIN_VALUE<=n) System.out.println("n is a: short"); else if (Integer.MAX_VALUE>=n && Integer.MIN_VALUE<=n) System.out.println("n is an: int"); else if (Long.MAX_VALUE>=n && Long.MIN_VALUE<=n) System.out.println("n is a: long"); } } ``` ``` Enter an integer: 100000 n is an: int ``` מספר שלם עובד לנו, אבל מה קורה במספר ממשי ``` Enter an integer: 10.5 Exception in thread "main" java.util.InputMismatchException at java.base/java.util.Scanner.throwFor(Scanner.java:939) at java.base/java.util.Scanner.next(Scanner.java:1594) at java.base/java.util.Scanner.nextInt(Scanner.java:2258) at java.base/java.util.Scanner.nextInt(Scanner.java:2212) at com.company.Main.main(Main.java:8) ``` קיבלנו Runtime error על הדרך בא נוסיף גם while ככה שכל עוד הקלט אינו 0 הוא ימשיך לבקש ```java import java.util.Scanner; public class Main { public static void main(String[] args) { System.out.print("Enter a number: "); Scanner scanner = new Scanner(System.in); double n = scanner.nextDouble(); while (n!=0.) { if (Short.MAX_VALUE >= n && Short.MIN_VALUE <= n && n % 1 == 0.) { System.out.println(n + " can fit in a: "); System.out.println("* short\n* int\n* long\n"); } else if (Integer.MAX_VALUE >= n && Integer.MIN_VALUE <= n && n % 1 == 0.) { System.out.println(n + " can fit in a: "); System.out.println("* int\n* long\n"); } else if (Long.MAX_VALUE >= n && Long.MIN_VALUE <= n && n % 1 == 0.) System.out.println(n + " can fit in a: \n* long\n"); else if ((Float.MAX_VALUE >= n && Float.MIN_VALUE <= n) || (Double.MAX_VALUE >= n && Double.MIN_VALUE <= n)) System.out.println("n is either a: float, double\n"); //receive next input System.out.print("Enter a number: "); n = scanner.nextDouble(); } scanner.close(); } } ``` ``` Enter a number: 10.5 n is either a: float, double Enter a number: 1000000 1000000.0 can fit in a: * int * long Enter a number: 0 ``` > גם היינו יכול לעשות `&& ((short) n) == n` ו `((int) n) == n` בתנאי > > יש לזה ביצועים יותר גבוההים --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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