COSC 111
MIDTERM 2
QUANTITATIVE SCIENCES COURSE UNION
qscu.org
Introductions
Name, Major, Role in QSCU
WHAT IS QSCU?
How do I get involved?
Weekly Meetings:
Tuesday, 9:00-9:30am PST
Discord - voice channel
OPEN TO EVERYONE!
(Snacks are sometimes provided)
How do I stay in the loop?
https://discord.gg/xH48R8K
Facebook.com/ubcoqscu
QSCU.org
LET’S GET STARTED
http://qscu.org/events/reviewmaterial/
1.
LOOPS
(for, while
nested fors,
etc.)
What is the output of the following code
fragment?
int num = 1, max = 20;
while (num < max) {
if (num%2 == 0)
System.out.print(num + “ “);
num++;
}
Answer: 2 4 6 8 10 12 14 16 18
Write a loop to print all the odd
numbers from 1 to 99 (inclusive)
Challenge: Answer this question
without a % operator
for(int i =1; i < 100; i++){
if(i %2 == 0){
System.out.println(i);
}
}
Challenge:
for(int i =1; i <= 99; i+=2){
System.out.println(i);
}
Transform the following while loop
into an equivalent for loop.
(Make sure it produces the same output)
int num = 1;
while (num < 20) {
num++;
System.out.println(num);
}
for(int i = 2; i <21; i ++){
System.out.print(i + “ “);
}
Increments then checks, because increment happens before the print we will
print 20
Pretty cool answer from the class:
for(int i = 1; i<20;)
System.out.println(++i);
Write a program that mimics a simple
slot machine in which three numbers
between 0 and 9 are randomly selected
and printed side by side.
Report to the user if all three of the
numbers are the same, or if any two of
the numbers are the same. Continue
playing until the user chooses to stop.
Assume the user gives valid input.
Scanner scan = new Scanner(System.in);
boolean play = true;
while(play){
int r1 = (int) (Math.Random()*10);
int r2 = (int) (Math.Random()*10);
int r3 = (int) (Math.Random()*10);
if( r1 == r2 && r2 == r3){
System.out.println(“all are the same”);
}
else if( (r1 == r2 && r2 != r3) || ( r1 == r3 && r2
!= r3) || ( r2 == r3 && r1 != r3)){
//handles case where first 2 same
//handles case where second 2 are same
// handles case where first and last
// helpful to draw out chart that i have
//The else if condition could also be !(r1 != r2 && r2!=r3 && r1 !=
r3)
System.out.println(“2 are the same”);
}
System.out.println(“would you like to play again?
Enter any number for yes and -1 for no”);
int check = scan.nextInt();
if(check == -1)
play = false;
}
Convert the following for loop to use a foreach
loop.
int[] x = {1, 2, 5, 7};
for (int i = 0; i < x.length; i++) {
System.out.println(x[i]);
}
Solution:
for (int i : x) {
System.out.println(i);
}
Create a for-each loop to output the
following numbers from an array:
Output:
12
13
14
44
int arr[]={12,13,14,44};
for(int i:arr){
System.out.println(i);
}
Convert the following for loop
into a do-while loop:
int sum = 0;
for(int i = 0; i < 10; i++){
sum += i;
System.out.println(sum);
int i = 0;
do {
sum += i;
System.out.println(sum);
i++;
}
while (i < 10);
Write a do-while loop that prints
every number that is divisible by
3 between 1 to 100 inclusive
int i = 0;
do {
if ( i % 3 == 0 ) {
System.out.println(i);
}
i++;
}
while ( i <= 100 );
Write a do-while loop to print
every element in numList where
int [] numList =
{1,2,3,4,5,6,7,8,9,10};
Answer:
int i = 0;
int [] numList = {1,2,3,4,5,6,7,8,9,10};
do {
System.out.println(numList[i]);
i++;
}
while (i < list.length);
2.
METHODS
Scope,
primitive vs
objects etc.
What is a static method (“class
method”)? What does the static
keyword do to a method or
variable?
Static methods can only modify static variables.
Any static variables or methods are shared by all instances of a class. So you can call a static method on
two different objects of the same class, but you will be calling the same method. The important thing to
note is that when you modify a static variable using a static method, that variable is changed for ALL
instances of the class.
1)
2)
3)
4)
Write the header to a method that takes input of
an int, two doubles and returns a decimal number.
Write the header to a method that takes a String
as input and returns a String.
Write the header to a method that takes no input
and returns nothing.
Write the header to a method that takes two
integers and any number of doubles (but can
accept more) and returns an array of decimal
1) public (double or float) foo (int a, double b, double c)
2) public String foo (String s)
3) public void foo ()
4) (int a, int b, double c, double…d) technically double…d can take zero
Method Overloading
For each foo method what would be the output
be?
public
public
public
Syntax
void foo(double a, int b){System.out.print("A");}
void foo(int a, double b, int c){System.out.print("B");}
void foo(int a, int b, double... c){System.out.print("C");}
error
Answers:
foo(1, 1); -> A or C depending
foo(1, 2.0); -> error
foo(1.0, 2); -> A
foo(1, 2, 3); -> B
foo(1, 2.0, 3); -> B
foo(1, 2, 3.0); -> C
foo(1, 2, 3, 4, 5); -> C
Variable Scope
Identify the error and suggest how to fix the following:
public static void main(String[] args) {
int n;
n = 3;
result = square(n);
System.out.println(n + " squared is: " + result);
n = 4;
result = square(n);
System.out.println(n + " squared is: " + result);
}
static int square(int i) {
int result = i * i;
return result;
}}
Ans. result is not defined in the main method, and is only defined locally in the square method
Variable Scope
Identify the error and suggest how you fix the following:
public static void main(String[] args) {
for(int i = 0; i < 10; i++) {
System.out.println(i * i);
}
double sqrt = Math.sqrt(i);
System.out.println(sqrt);
}
Ans. A variable, i, cannot be called outside of a loop, as it is only defined locally within a loop. The
line double sqrt = Math.sqrt(i); calls on a variable, i, that is not resolved
Write a method called powersOfTwo that
prints the first 10 powers of 2. Starting with
2. (22 , 23, 24… 210)
The method takes no parameters and has
no return value.
public static void powersOfTwo(){
for(int i =2; i <= 10; i ++)
print(Math.Pow(2,i);
}
Write a method called multiConcat that takes a
String and an integer as parameters.
Return a String that consists of the string
parameter concatenated with itself count times,
where count is the integer parameter. For example, if
the parameter values are “hi” and 4, the return value
is “hihihihi” . Return the original string if the integer
parameter is less than 2.
public static String multiConCat(String s, int count){
String r ;
if(count < 2){
Return s;
}
for(int i = 0 i < count; i ++){
R += s;
}
Return r;
}
Write a method called randomInRange that
accepts two integer parameters representing
a range. The method should return a random
integer in the specified range (inclusive).
Return zero if the first parameter is greater
than the second.
public static int randomInRange(int max, int min){
if( max > min ){
return 0;
}
Random rand = new Random();
Return random.nextInt((max-min) +1) + min;
//or
Int x = (int) ( ( (Math.random() * ( (max - min ) + 1)) ) + min) ;
return x;
// between 5 and 14, 14-5 is 9 so random from 0 to 9 and + 5 to make up to 14
// add one because exclusivity of random generator
Write a method called average that
accepts two integer parameters and
returns their average as a floating
point value.
Public static double average(int a , int b){
Double x = (a+b)/2;
Return x;
}
Overload the average method such that if
three integers are provided as parameters, the
method returns the average of all three
Overload the average method to accept four
integer parameters and return their average.
Public static double average(int a , int b){
Double x = (a+b)/2;
Return x;
}
Public static double average(int a , int b, int c, int d){
Double x = (a+b + c + d)/4;
Return x;
}
Public static double average(int a , int b, int c){
Double x = (a+b +c)/3;
Return x;
}
3.
Arrays
Reference Data
What does the following code snippet print out?
What if the array was of type boolean?
int [] array = new int[10];
for(int i = 0; i < array.length; i++)
System.out.println(‘array at” +
i + “ is “ + array[i]);
Array at 0 is 0 (if boolean false)
……
Array at 9 is 0
What is the output for the
following code?
public class Test {
public static void main(String[] args) {
int[] x = {1, 2, 3, 4};
x = new int[2];
for (int i = 0; i < x.length; i++)
A)
B)
C)
D)
1
1
0
1
System.out.print(x[i] + " ");
}
}
C
Initialize all array elements with 0
2
2 3 4
0
1
Create an array of words (I called mine “words”), and write a
method for each of the following
1.
2.
3.
Find the word in the array with the most vowels (remember
to count upper and lower case!)
Replace the first letter of every word with “B”
(BONUS!) Sort the array alphabetically (don’t use the
Arrays.sort method)
The following code aims to print the elements of the array
nums as well as the value of the counter i which causes
the loop to terminate. The code includes 3 errors. Find
these errors and rewrite the code after fixing them.
double nums[] = {1.5, 2.3, 3.6};
for (int i = 0; i <= nums.length; i++) {
System.out.println(nums);
}
System.out.println(i);
Errors:
1. index not specified on nums -> should be nums[i]
2. The call to print out is outside the scope of i
3. Nums.length needs to be -1 or < as it creates an index out of bounds exception once print
To fix, specify index of nums (nums[i]) and declare i outside of loop. ( int i; )
Create a multiplication table. Use
multidimensional arrays.
int[][] mult = new int[9][9];
for(int i = 0; i < mult.length; i++){
for(int j = 0; j<mult[i].length; j++){
mult[i][j] = (i+1)*(j+1);
}
}
for(int k = 0; k < mult.length; k++){
for(int l = 0; l < mult.length; l++){
System.out.printf("%3d", mult[k][l]);
}
System.out.println();
}
Given a 2D array A, transform it into
array B by moving each row.
Remember a 2D array is an array of
1D arrays.
A
1
5
9
13
2
6
10
14
3
7
11
15
B
4
8
12
16
16
12
8
4
15
11
7
3
14
10
6
2
13
9
5
1
public static int [][] transform ( int [][] array ) {
int row = array.length;
int col = array[0].length;
int [][] result = new int [row][col];
for ( int i = 0; i < row; i++ ) {
for ( int j = 0; j < col; j++ ) {
result[i][j] = array[(row-1)-i][(col-1) -j];
}
}
return result;
}
GOOD LUCK!