Learning Goals

By the end of this week, you will be able to:
  1. Identify and understand variable types and operations on variables
  2. Implement variables and operations in a C++ program to solve a computational problem
  3. Write arithmetic expressions and assignment statements in C++
  4. Appreciate the importance of comments and good code layout
  5. Create programs that read and process input, and display the results

CONTENTS:

    

Readings

Please note the advised readings of “Brief C++ Late Objects” - Cay Horstmann:

  1. Monday: Martin Luther King Jr. Day (classes canceled)
  2. Wednesday: 2.5, 7.3
  3. Friday: 3.1, 3.2, 3.7

    

Background

Variables and Operators

This week we learned about variables and basic arithmetic operators in computer science.

Variables in computer science are similar to variables you have seen in other math and science courses. A variable is a value that can change, depending on conditions or on information passed to the program.

A computer stores variables differently depending on the type of information they are meant to contain, so we must declare the type of variable. This table will tell you the names of different types of variables in C++:

Type of variable Declaration in C++ Size Description Example
Integer int 2 or 4 bytes a number that has no decimal value -42
Float float 4 bytes a number that has short decimal values 2.98
Double double 8 bytes a number that can have longer decimals 2.98<...>
Character char 1 byte stores a single letter/character using ASCII values 'h'
Boolean bool 1 byte stores either True or False true 
// Here is an example of declaring variables:
int myNumber = 0;
double myDecimal = 3.1415;
char myEmptyChar;

After declaring variables, you can access them without repeating their data type. You can also perform basic operations, including the ones listed in this table:

Operator Description Example
+ Adds together two values x + y
+= Adds to itself and stores the new value x += y
- Subtracts one value from another x - y
* Multiplies two values x * y
/ Divides one value by another x / y
% Modulus; this returns the division remainder x % y
++ Increment; this increases the value of a variable by 1 ++x
-- Decrement; this decreases the value of a variable by 1 - 
// Here is an example of declaring variables and using operators:
int myNumber = 4;
int mySecondNumber = 5;
int mySum = myNumber+mySecondNumber;
int myThirdNumber = 6;
mySum = mySum + myThirdNumber;
int myFourthNumber = 7;
mySum += myFourthNumber;
// By the end of this code, the variable `mySum`
// would contain `4+5+6+7`, or rather, `22`.

   

Characters

Characters are a variable type that is made of a single byte, which means they can encode for a fairly limited number of characters. We can identify which characters we can store using an ASCII table shown below.

Characters can be referred to by placing the chosen character in single quotation marks, like this:

char myChar = 'a';

Characters can also can be accessed using numerical values. Since every sequence of binary numbers that encodes a character could also instead be interpreted as an integer, we can use those numbers to identify which character we are talking about. The integer values that correspond with each letter are shown in the ASCII table.

There are a few traits that you may find helpful as you move forward: firstly, observe that all lower case letters are listed in consecutive alphabetical order, and secondly that all upper case letters are similarly listed in consecutive alphabetical order. This means that the space between a lowercase ‘a’ and a capital ‘A’ is the same as the space between a lowercase ‘b’ and a capital ‘B’ and so on. This is useful for converting characters from lowercase to uppercase.

ascii table 0 Null to 127 Del, must lookup an accessible table

   

Strings

In C++, a string is a data type that represents sequences of characters instead of a numeric value (such as int or float). A string literal can be defined using double-quotes. So "Hello, world!", "3.1415", and "int i" are all strings. We can access the character at a particular location within a string by using square brackets, which enclose an index which you can think of as the address of the character within the string. Importantly, strings in C++ are indexed starting from zero. This means that the first character in a string is located at index 0, the second character has index 1, and so on. For example:

string s = "Hello, world!";
cout << s[0] << endl;  //prints the character 'H' to the screen
cout << s[1] << endl;  //prints the character 'e' to the screen
cout << s[4] << endl;  //prints the character 'o' to the screen
cout << s[9] << endl;  //prints the character 'r' to the screen
cout << s[12] << endl; //prints the character '!' to the screen

Note that when a character in a string is accessed with square brackets, the character has type char. For example:

string str = "Example"; //this is a string
char c = str[1]; //this is a char

There are many useful standard functions available in C++ to manipulate strings. One of the simplest is length(). We can use this function to determine the number of characters in a string.

string s = "Hello, world!";
int s_length = s.length();
cout << s_length << endl; //This line will print 13 to the screen

Notice how the length function is called.

The correct way:

s.length()

Common incorrect ways:

length(s)  // NO: if only it were so simple...
s.length   // NO: don't forget the ()

Another useful function available for strings is substr(). This function allows us to access a subset, or a small portion, of a longer string. The substring function takes two arguments:

  1. The starting index of the substring you would like to capture
  2. The length of the substring you would like to capture (optional)

Note that the second argument is optional. If you don’t pass a second argument to subtring, then the function will print the entirety of the string, beginning with the character at the position specified in the first argument. Note that substr() always returns a variable of type string, regardless of the length of the substring.

For example, consider the code below:

   
// Substring example code:
string str = "Coding is fun!";
cout << str.substr(0, 6) << endl;
cout << str.substr(6) << endl;
cout << str.substr(1, 1) << endl; //prints a string of length one

This will ouput the following:

Coding
 is fun!
o

Note: The second line of output begins with a space.

Both length() and substr() are special kinds of functions associated with objects, usually called methods, which we will discuss later in the course.

   

Terminal Input and Output

It is important to be able to take input from the user or to print output to the terminal as your program runs. You can do this using cin and cout for input and output, respectively.

The Hello World program you have seen provides an example of using cout to display output.

// EXAMPLE: Hello World for C++:
#include <iostream>

using namespace std;

int main() {
    cout << "Hello, world!" << endl;
    
    return 0;
}

You can similarly ask the user for a particular value and store that value in a variable using cin:

// EXAMPLE: An example of collecting user input to sum two integer variables and then printing their sum
#include <iostream>

using namespace std;

int main() {
    int firstNum;
    int secondNum;
    cout << "Please provide one number:" << endl;
    cin >> firstNum;
    cout << "Please provide a second number:" << endl;
    cin >> secondNum;
    cout << "The sum of these two numbers is " << firstNum + secondNum << endl;

    return 0;
}

   

Pseudocode and Algorithms

Pseudocode is used to develop algorithms. An algorithm is a procedure for solving a problem.

An algorithm describes actions to be executed and the order in which those actions are to be executed. In other words, an algorithm is merely the sequence of steps taken to solve a problem; like a recipe. An algorithm is not computer code. Algorithms are just the instructions which provide a clear path for you to write the computer code.

An algorithm for adding two numbers together:
  1. Step 1: Start
  2. Step 2: Declare variables num1, num2, and sum.
  3. Step 3: Read values num1 and num2.
  4. Step 4: Add num1 and num2 and assign the result to sum.
  5. Step 5: Display sum
  6. Step 6: Stop

The main difference between an algorithm and pseudocode is that an algorithm is a step by step procedure to solve a given problem while pseudocode is a method of writing an algorithm. In other words, an algorithm is how to solve a problem while pseudocode is how to implement that solution.

Algorithm Pseudocode
An unambiguous specification of how to solve a problem. An informal high-level description of the operating principle of a computer program or other algorithm.
Helps to simplify and understand the problem. A method of developing an algorithm.

Pseudocode is informal language that helps programmers develop algorithms (or recipes). Although there are no hard and fast rules for pseudocode, there are some suggestions to help make pseudocode more understandable and easy to read.

For instance, consider indenting all statements showing a “dependency”, like statements that use: While, do, for, if.

Several keywords are often used to indicate common input, output, and processing operations.

Term A Few Equivalent Terms
Input: READ, OBTAIN, GET
Output: PRINT, DISPLAY, SHOW
Compute: COMPUTE, CALCULATE, DETERMINE
Initialize: SET, INITIALIZE
Add one: INCREMENT, BUMP

For looping and selection, the keywords that you might consider writing include:

  1. Do While…
  2. Do Until…
  3. Case…
  4. If… then…
  5. Call … with (parameters)
  6. Call
  7. Return ….
  8. Return
  9. When

Try to indicate the end of loops and iteration by using scope terminators. For instance use if… (statements) ... endif.

Other words you may find useful while writing pseudocode include: Generate, Compute, Process, set, reset, increment, compute, calculate, add, sum, multiply, subtract, divide, print, display, input, output, edit, test, etc.

Be sure to indent if the indentation fosters understanding. Being clear is the purpose of pseudocode, and a very desirable goal to strive for.

Here are some examples of pseudocode:

 
// Will a grade pass?
/**
 * If students course grade is lower than  60
 *    Then Print, "Failed"
 * else
 *     If students exam grade is lower than  67
 *         Then Print, "Failed"
 *     else
 *         Print, "Passed"
 *     endif
 * endif
 */
 
// How do you find the area of a rectangle?
    // Read the length of the rectangle
    // Read the width of the rectangle
    // Compute the area of the rectangle as length times width.

You should write pseudocode whenever you are addressing problems in computer science. This allows you space to determine how to solve a problem without worrying about syntax and formatting, instead of having to figure out everything all at once.

    

Homework

You should complete the following homework using VSCode and the skills that you have learned to author, compile, and execute programs. You should build and fix your code using VSCode. Once you believe you have completed the assignment locally, submit your work on Canvas using the appropriate link for the assignment and the “coderunner” tool.

The coderunner questions match these questions exactly. It will tell you what to do for the problem, give you a few examples of input/output. Give you a space to submit your code.

Be sure to press the check button. This will run your code against many tests, including some new ones that we didn’t give you as examples. If you are failing any of those tests, use the information about the exact test you are failing, return to VSCode, and fix the code before continuing to do work on coderunner.

Be sure to backup your files.

   

Identify and Correct the Errors

There are several snippets of code below where there is one error. You will need to identify and correct the error so that the code compiles. This code is also available directly in CodeRunner.

  

Problem 1 Spot the error(s):

HINT: there is only one error.

#include <iostream> 
using namespace std;

int Main()
{
    cout << "Hello, World!" << endl;
    return 0; 
}

  

Problem 2 Spot the error(s):

#include <iostream> 
using namespace std;

int main 
{
    cout << "Hello, World!" << endl;
    return 0; 
}

  

Problem 3 Spot the error(s):

#include <iostream> 
using namespace std;

int main() 
{
    cout << "Hello, World! << endl;
    return 0; 
}

  

Problem 4 Spot the error(s):

HINT: there are multiple errors

#include <IOstream> 
using namespace std;

int main() 
{
    cout << "Hello, World!" << endl
    return 0; 
}

  

Problem 5 Spot the error(s):

#include <iostream> 
using namespace;
int main() 
{
    cout << "Hello, World!" < endl; 
}

   

Problem 6 Fahrenheit to Celsius Converter

Create a program that convert temperatures from Fahrenheit to Celsius.

Celcius is equal to fahrenheit minus thirty-two quantity times quantity five over nine

PROTIP: Don’t copy and paste the above equation into your VSCode, it tends to have special characters that cause weird behaviors.

The answer-box in coderunner is pre-loaded with following solution template for this question.

#include <iostream>

using namespace std;

int main(){
    // declare all the variable
    double fahrenheit, celsius;

    // prompt the user & get their input
    cout << "<add question>" << endl; // EDIT THIS LINE TO PROMPT USER
    cin >> fahrenheit;

    // temperature calculation
    celsius = <add equation>; // EDIT THIS LINE TO CALCULATE TEMPERATURE
    // hint: use (5.0/9.0) instead of (5/9)

    cout << "The temperature is " << celsius << " degree Celsius." << endl;
    return 0;
}

Here are a few sample runs of the program, with user input shown in red:

What is the temperature in Fahrenheit?

32

The temperature is 0 degree Celsius.

   

Problem 7 Calculate the Falling Time of an Object

Let’s build our own programs now. Start by writting comments describing what you want to do. Then move toward an algorithm as psudo code. After that, you are ready to write your code. This one might be a bit tricky.

Create a program that calculates the time for a falling object to hit the ground based on the height from which the object fell. The equation for this is:

time is equal to the square-root of two times height quantity over nine-point-eight

  1. time: is the amount of time the object fell in seconds.
  2. height: is the height the object was dropped from in meters.

Hint: the cmath library for C++ contains a square root function that you can utilize.

You should print the time to two decimal places. You can accomplish this by using the iomanip library and the setprecision function (google is you friend). Here is a sample run of the program:

How far did the object fall in meters?

4

The object fell for 0.90 seconds.

   

Problem 8 Volume Of A Fish Tank

Write a program that calculates the volume of a fish tank. Ask the user for three values: the length, the width, and the height of the tank in inches. Use these values to calculate the total volume of the tank in cubic inches. Then, translate cubic inches into gallons and tell the user how many gallons can fit in the fish tank. Print this capacity to one decimal place.

Hint: 1 cubic inch is 0.004329 gallons.

What is the length of the fish tank in inches?

20

What is the width of the fish tank in inches?

20

What is the height of the fish tank in inches?

20

This fish tank has a 34.6 gallon capacity.

   

Problem 9 Pool Water Management

You’re in charge of maintaining a swimming pool with a minor leak. The pool has some water in it already and needs to be filled up. However, due to the leak, the water level decreases slightly every hour at a constant rate. Write a program takes the hour as an input (as an integer or a double - you choose) and predicts the pool’s water level over time.

Pool Initial water level (inches) Fill rate (inches/hour) Leakage rate (inches/hour)
Indoor Pool 19 0.6 0.4
Outdoor Pool 22 0.3 0.1

How many hours have passed?

22

The indoor pool has 23.4 inches of water, and the outdoor pool has 26.4 inches of water.

   

Problem 10 Barter System

Bartering is the exchange of goods and services between two or more parties without the use of money. Below is the table of conversion values:

Items Values
1 chicken 6 avocados
1 avocado 2 watermelon
1 watermelon 4 potatoes

1 chicken is equal to 6 avocados, 1 avocado is equal to 2 watermelon, and 1 watermelon is equal to 4 potatoes.

Your program should take the number of potatoes as an input(integer) and converts its value to the maximum number of chickens, avocados, watermelons, and potatoes that can be bought. Note that you must buy the highest value item(s) first.

Enter the number of potatoes:

200

Maximum number of chicken(s) 4, avocado(s) 1, watermelon(s) 0, potato(es) 0

Enter the number of potatoes:

100

Maximum number of chicken(s) 2, avocado(s) 0, watermelon(s) 1, potato(es) 0

   

Entering on coderunner

Now that you have completed all of the assignment in VSCode, go submit your work via coderunner on Canvas. Be sure to check your work and return to VSCode as needed if you need to fix anything. Don’t forget to submit this work on coderunner by the deadline to receive credit for this assignment.