update,

2025-02-01 01:58:47 +08:00
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+## Q1
+(a) (4 marks) Name the most suitable primitive data types in Java that can store the
+following data:
+
+(1) the price of a notebook computer (e.g. 6888.5)
+
+(2) the number of visits to Facebook in 2019 
+
+```
+(1) double
+(2) int
+```
+
+(b) (5 marks) Identify whether the statments below are valid in Java.
+| code | valid | invalid |
+| ---- | ----- | ------- |
+| byte b = 12.2; | [] | [v] |
+| double x = (int) 28.05; | [v] | [] |
+| float f = 26.0; | [] | [v] |
+| char c = "c"; | [] | [v] |
+| int[3] arr = {1, 2, 3}; | [] | [v] |
+
+(c) (4 marks)
+
+(1) What is the size (number of bytes) of a float variable?
+
+(2) What is the size (number of bytes) of a long variable? 
+
+```
+(1) 32(bits)/8 = 4 bytes 
+(2) 64(bits)/8 = 8 bytes
+```
+
+(d) (4 marks) Identify whether the identifier names below are valid in Java.
+
+| code | valid | invalid |
+| ---- | ----- | ------- |
+| $12_3 | [] | [v] |
+| a:b | [] | [v] |
+| 4x | [] | [v] |
+| Java | [v] | [] |
+
+## Q2
+
+(9 marks) Given x, y and z are integers and x = 2, y = 3 and z = 8, write down the output of
+the following statements:
+
+(a) System.out.println( "\\\""+x+"\"\\" );
+```
+Answer: 
+\""\
+```
+(b)
+System.out.println( x+y+"\t"+z+"\n"+y+z+"\t"+x );
+```
+Answer: 
+5   8
+38  2  
+```
+(c) 
+z += (x+z)/y - (x+z)%y;
+System.out.println(z);
+```
+Answer:
+10
+```
+
+## Q3
+(9 marks) What will be printed by the program fragment below?
+```
+int x=3, y=7, z=4;
+z = --x + y++;
+System.out.println("x=" + x);
+z = x-- + y++ + z;
+System.out.println("y=" + y);
+System.out.println("z=" + z);
+```
+```
+Answer:
+x=2
+y=9
+z=19
+```
+
+## Q4
+(a) (6 marks) Write a Java program statement to declare and initialize a variable/constant
+for each of the cases below. The identifier names MUST be meaningful and follow Java
+convention.
+
+(1) A variable to store the average mark of a student in a semester, with initial value 0.0.
+```
+Answer: double avgMark = 0.0;
+```
+(2) A constant to represent the maximum number (value 10) of items a user can borrow.
+```
+Answer: final int maxBorrowNum = 10;
+```
+
+(b) (4 marks) Rewrite the following Mathematical equation in Java. Assume that all variables
+in the equation are of double type and initialized properly.
+```
+Answer: double x = (x + (y/6)) / (3 * (x * x - 1))
+```
+
+## Q5
+(a) (4 marks) What is the output of the following statements:
+```
+int x = 2, y = 5;
+if ( !(x>y && x<=y) && x>y)
+System.out.println("AAA");
+else
+System.out.println("BBB");
+System.out.println( (x<=3 || !(y!=7)) ? "XXX" : "YYY");
+```
+
+```
+Answer: 
+BBB
+XXX
+```
+
+(b) (2 marks) Consider the following statements.
+```
+if (i==20 || i==50 || i==60)
+j=1;
+else if (i==10 || i==30)
+j=2;
+else
+j=3;
+System.out.println("j=" + j);
+```
+(1) What is the output of the above statements if i has the value 30.
+(2) What is the output of the above statements if i has the value 33.
+
+```
+Answer: 
+(1) j=2
+(2) j=3
+```
+
+(c) (6 marks) Rewrite the above if-else statement using a switch structure.
+```
+Answer:
+
+switch(i){
+    case 20:
+    case 50:
+    case 60:
+        j = 1;
+        break;
+    case 10:
+    case 30:
+        j=2;
+        break
+    default:
+        j=3;
+}
+```
+## Q6
+(14 marks)
+
+(a) (1) What is the output of the following program segment?
+```
+int a=10, x=0;
+do {
+    a-=1;
+    x+=2;
+    if (a<=6)
+    break; //(*)
+} while (a>4);
+System.out.println("x=" + x);
+```
+(2) What is the output if the word break at the line marked with (*) is changed to
+continue?
+
+```
+Answer:
+(1) x=8
+(2) x=12
+```
+
+(b)
+Complete the following program fragment which prints a pattern as below. The number
+of lines in the pattern is determined by the int variable numLine.
+```
+Output:
+// numLine is 3
+531
+ 31
+  1
+// numLine is 5
+97531
+ 7531
+  531
+   31
+    1
+
+Answer:
+int numLine;
+// code skipped - read the value of numLine
+for (int i= numLine; i>=1; ____i--_____) {
+    // print space
+    for (int j=1; j<=____numLine - i____; ___j++____)
+    System.out.print (____" "____);
+    // print numbers
+    for (int j=i; j>=___1___; ___j--____)
+    System.out.print (____j*2-1_____);
+    // advance a line
+    System.out.____println_____();
+}
+```
+
+## Q7
+(a) (6 marks) Write a for-loop to find and print the integer answer of the mathematical
+expression: 2×5 - 3×7 + 4×9 - 5×11 + 6×13 - 7×15
+You only need to write statements for variable declaration(s), the loop and the output
+statement. You are NOT required to write a complete Java program.
+
+```
+Answer:
+int answer = 0;
+for(int i = 2, j = 5; i <=7 && j <=15; i++, j+=2)
+    if (i % 2 == 0)
+        answer += i*j;
+    else
+        answer -= i*j;
+System.out.println(answer);
+```
+
+(b) (9 marks)
+(1) Write ONE statement to declare an array with the following settings:
+```
+Array variable: quotas 
+Data type: int
+Size: 5 
+elements Values: 1, 2, 3, 4, 5
+```
+```
+int[] quotas = {1,2,3,4,5};
+```
+
+(2) What is the value of quotas.length? 
+```
+5
+```
+
+(3) Write a for loop to find the average value in the array quotas and store the result in
+mean.
+```
+int sum = 0;
+double mean;
+for(int i = 0; i < quoatas.length; i++)
+    sum += quotas[i];
+mean /= quotas.length;
+```
+
+(4) Write a for loop to add 2 to all the elements in the array quotas.
+```
+for(int i = 0; i < quotas.length; i++)
+    quotas[i] += 2;
+```
+
+## Q8
+(14 marks) Complete the program below which calculates the shipping cost of a courier
+service. The cost is calculated by weight×rate, where rate is based on weight as shown in
+the table below.
+
+| weight (in kg) | rate ($ per kg) |
+| -------------- | --------------- |
+| weight >= 50 | 18 |
+| 50 > weight >= 40 | 20 |
+| 40> weight >=20 | 25 |
+| weight < 20 | 30 |
+
+Shown below is a sample execution of the program. Those in bold underline are user inputs.
+Your program MUST check whether the weight inputted is greater than or equal to zero, or
+otherwise print an error message and ask the user to input again. You may assume user will
+always input an integer for the variable weight. The program will repeat running until the
+user inputs zero (0).
+
+```
+C:\> java ShippingCost
+Enter weight: -12
+Invalid input! Please input again.
+Enter weight: 55
+The shipping cost is 990
+Enter weight: -6
+Invalid input! Please input again.
+Enter weight: 30
+The shipping cost is 750
+Enter weight: 0
+Thank you for using this program. Bye!
+```
+```
+import java.util.Scanner;
+public class ShippingCost {
+    public static void main( String[] args ) {
+        int weight; // parcel weight - inputted by user
+        int rate=0; // shipping rate - determined by the value of weight
+        Scanner input = new Scanner( System.in );
+        while (true) {
+
+            // Answer:
+
+            weight = input.nextInt();
+            if (weight == 0)
+                break;
+            
+            if (weight < 0)
+                System.out.println("Invalid input! Please input again.");
+            else{
+
+                if (weight >= 50)
+                    rate = 18;
+                else if (weight >= 40)
+                    rate = 20;
+                else if (weight >= 20)
+                    rate = 25;
+                else
+                    rate = 30;
+                
+                System.out.println("The shipping cost is " + (weight * rate));
+
+            }
+
+
+        } // while (true) - end
+        System.out.println("Thank you for using this program. Bye!");
+    }
+}
+```