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+# Lab 2 Variables and Arithmetic Operations
+
+### Intended Learning Outcomes
+
+Upon completion of this tutorial/lab, you should be able to:
+- Define variables with meaningful names.
+- Use arithmetic expressions and assignment statements to perform calculations.
+- Identify and fix syntax errors in Java programs.
+
+## Exercise 1
+Identify whether the followings are valid or invalid identifiers.
+
+| variable name | Valid | Invalid |
+| ------------- | ----- | ------- |
+| R2D2 | [x] | [] |
+| Watchamacallit | [x] | [] |
+| howAboutThis? | [] | [x] |
+| Java | [x] | [] |
+| GoodChoice | [x] | [] |
+| 12345 | [] | [x] |
+| 3CPO | [] | [x] |
+| This is okay | [] | [x] |
+| thisIsReallyokay | [x] | [] |
+| aPPlet | [x] | [] |
+| Bad-Choice | [] | [x] |
+| A12345 | [x] | []|
+
+## Exercise 2
+Write down the output of the program fragments below.
+```
+double amount;
+amount = 20;
+System.out.println(amount – 8);
+
+# Output: 12.0
+```
+
+```
+int n=9;
+n+=1;
+System.out.println(n);
+System.out.println(n+1);
+
+# Output: 
+10
+11
+```
+
+```
+int num=7;
+num = 9%num;
+System.out.println(num);
+
+# Output: 2
+```
+
+```
+int u, v;
+u = 5;
+v = u * u;
+System.out.println(u*v);
+
+# Output: 125
+```
+
+```
+double x=8;
+x += 5;
+System.out.println(x + 3 * x);
+
+# Output: 52
+```
+
+```
+double p=5.1, q=2.3;
+p += p;
+System.out.println(p + q);
+System.out.println(p – q);
+
+# output: 
+12.5
+7.9
+```
+
+### Exercise 3
+Identify the errors in the following Java program fragments.
+
+(a)
+```java
+// Question
+double a, b, c;
+a = 2;
+b = 3;
+a + b = c;
+System.out.println( 5((a + b) / (c + d);
+``` 
+```
+// Answer
+"a + b" = c;
+```
+* only a variable is allowed on the left hand side of an assignment statement
+```
+System.out.println( 5"*"((a + b) / (c + "d")"))";
+```
+* \* is expected between 5(
+* d was not declared
+* two ) were missed
+  
+
+(b)
+```java
+// Question
+double balance, deposit;
+balance = 1,200.3;
+deposit = $140;
+System.out.println( balance + deposit );
+```
+
+```
+// Answer
+balance = 1","200.3;
+```
+* comma is not allowed
+
+```
+deposit = $140;
+```
+* $ is not allowed
+
+(c)
+```java
+// Question
+double 6n; 
+6n = 2 * 6n;
+```
+```
+// Answer
+double "6n";
+```
+* a variable name must start with a letter (not a digit)
+
+## Exercise 4
+Write down the output of the program fragments below.
+```java
+String var;
+var = "Programming";
+System.out.print( var );
+var = "Networking";
+System.out.println( var );
+
+// Output:
+ProgrammingNetworking
+```
+
+```java
+System.out.println( "act" + "ion" );
+
+// Output: action
+```
+
+```java
+double var1 = 3;
+System.out.println( var1 + 5 );
+
+// Output: 8.0
+```
+
+```java
+System.out.println("The price is " + 30 + " dollars and " + 60 + " cents." );
+
+// Output:
+The price is 30 dollars and 60 cents.
+```
+
+## Exercise 5
+```java
+public class StringConcatenate {
+
+    public static void main(String[] args) {
+
+        int number1 = 200;
+
+        int number2 = 8;
+
+        int number3 = 18;
+
+        System.out.println("Next year is " + number1 + number2);
+
+        System.out.println("My age is " + (number2 + number3));
+
+    }
+
+}
+
+// Output:
+Next year is 2008
+My age is 26
+```
+
+## Exercise 6
+
+```java
+public class IncrementDecrement {
+   public static void main( String[] args ) {
+      int a, x;
+      a = 10;
+      x = a++;
+      System.out.println( "a=" + a );
+      System.out.println( "x=" + x );
+      x = ++a;
+      System.out.println( "a=" + a );
+      System.out.println( "x=" + x );
+   }
+}
+
+// Output:
+11
+10
+12
+12
+```
+## Exercise 7
+Can the following conversions involving casting be allowed? If so, find the converted result, that is, the value stored in variable $i$.
+
+```java
+char c = 'A';
+int i = int (c);
+
+// not allowed
+```
+
+```java
+double d = 1000.74;
+int i = (int) d;
+// allowed, 1000
+```
+
+```java
+boolean b = true;
+int i = (int) b;
+
+// not allowed
+```
+
+## Exercise 8
+PROBLEM: Calculate the volume of a cylinder (with console I/O)
+
+Write a Java program that computes the volume ($v$) of a cylinder. The program should use Scanner class to read the radius ($r$) and the length ($l$), and compute the volume ($v$) with the formula: $v = r^2\pi l$.
+
+Test Case
+|  | Case 1 | Case 2 | Case 3 |
+| - | - | - | - |
+| $r$ | 4 | 6 | 8 |
+| $l$ | 5 | 7 | 9 |
+| $v=$ | 251/3274 | 791.6813 | 1809.5574 |
+
+```
+c:\> java Ex8
+Enter r : 8
+Enter l : 9
+v = 1809.5574
+```