Jam 2: Study Guide

Jams are open book. 40 minutes in lab.

Topics:

This quiz includes the previous topics from Jam 1 plus

  • Conditional statements: if/else

  • Logical and relational operators: &&, ||, !, ⇐, >=, >, < , ==

  • Arithmetic operators: +, -, , /, ++, --, += , -=, =, /=

  • String comparisons, the empty string: ""

  • loops: for- and while-

  • Accumulator variable pattern

Write Java programs to check your answers. Or you can ask a TA or instructor to give feedback on your responses.

Practice questions

1) Given the following variables, what is the value and type for each of the following expressions?

int x = 5;
int y = 13;
String message = "cat!";
boolean Done = false;

  • x < 10 && y < 10

  • x < 10 || y < 10

  • x < 10 && x > 0

  • x > 10 || x < 0

  • (5/x) > 7.0

  • message.compareTo("cats") == 0

  • !Done

  • Done || (x < 6 && y > 10)

2) Consider the following code

String colorName = "purple";

if (colorName.compareTo("red") != 0) {
  System.out.println(colorName + " is not primary");
}
else if (colorName.compareTo("blue") != 0 {
  System.out.println(colorName + " is not primary");
}
else if (colorName.compareTo("yellow") != 0) {
  System.out.println(colorName + " is not primary");
}
else {
  System.out.println(colorName + " is primary");
}

  • Draw a decision diagram corresponding to this if statement.

  • What does the above code print when

    • colorName = "purple"?

    • colorName = "red"?

    • colorName = "yellow"?

3) Write a program that inputs a month as an integer and returns a string name for that month. For example, if we call the function with the number 1, the program should print "January".

$ java Month
Enter an integer: 1
January

$ java Month
Enter an integer: 10
October

4) Consider the following loop

int pinLength = 4;
String pin = "";
for (int i = 0; i < pinLength; i++) {
  pin = pin + "*";
  System.out.println(pin);
}
System.out.println("Enter your pin: "+pin);

  • What is output to the console when we run this program?

  • Convert the loop above so it uses a while loop instead of a for loop

5) Show the output from the following code fragment:

for (int x = 0; x < 6; x++) {
  System.out.println(x + " " + x*x);
}
System.out.println("done!")

6) Consider the following program

int x = 3;
System.out.println("0  " + x);
for (int i = 0; i < 5; i++) {
    if (x % 2 == 0) {
        x = x / 2;
    }
    else {
        x = ( 3*x + 1 ) / 2;
    }
    System.out.println(i + " " + x);
}

  • Trace the program and show its output.

  • Create a table having columns for i, and x and show how the values change as the loop executes.

7) Write a program that asks the user how many grades they want to average, prompts the user for those grades, and prints the average.

Enter number of grades to average: 5

Enter grade: 96
Enter grade: 86
Enter grade: 76
Enter grade: 66
Enter grade: 56

Average is: 76.0

8) Write a program that asks the user for a word, and then uses an accumulator to print out the word with all lowercase "e"s changed to uppercase "E"s.

Enter a word: repetitive

rEpEtitivE