4.x — Chapter 4 summary and quiz

Quick Review

The smallest unit of memory is a binary digit, also called a bit. The smallest unit amount of memory that can be addressed directly is a byte. The modern standard is that a byte equals 8 bits.

A data type tells the compiler how to interpret the contents of memory in some meaningful way.

C++ comes with support for many fundamental data types, including floating point numbers, integers, boolean, chars, null pointers, and void.

Void is used to indicate no type. It is primarily used to indicate that a function does not return a value.

Different types take different amounts of memory, and the amount of memory used may vary by machine. See 4.3 -- Object sizes and the sizeof operator for a table indicating the minimum size for each fundamental type.

The sizeof operator can be used to return the size of a type in bytes.

Signed integers are used for holding positive and negative whole numbers, including 0. The set of values that a specific data type can hold is called its range. When using integers, keep an eye out for overflow and integer division problems.

Unsigned integers only hold positive numbers, and should generally be avoided unless you’re doing bit-level manipulation.

Fixed-width integers exist to define integer types with guaranteed sizes. Favor the std::int_fast#_t and std::int_least#_t integers when you need a fixed size guaranteed to be at least a certain size. std::int8_t and std::uint8_t should generally be avoided, as they tend to behave like chars instead of integers.

size_t is an unsigned integral type that is used represent the size of length of objects.

Scientific notation is a shorthand way of writing lengthy numbers. C++ supports scientific notation in conjunction with floating point numbers. The digits in the significand (the part before the e) are called the significant digits.

Floating point is a set of types designed to hold real numbers (including those with a fractional component). The precision of a number defines how many significant digits it can represent without information loss. A rounding error can occur when too many significant digits stored in a floating point number that can’t hold that much precision. Rounding errors happen all the time, even with simple numbers such as 0.1. Because of this, you shouldn’t compare floating point numbers directly.

The boolean type is used to store a true or false value.

If statements allow us to execute one or more lines of code if some condition is true. Multiple statements can be executed if they are put inside a block (inside curly braces). The conditional expression of an if statement is interpreted as a boolean value.

Char is used to store values that are interpreted as an ASCII character. When using chars, be careful not to mix up ASCII code values and numbers. Printing a char as an integer value requires use of static_cast.

Angled brackets are typically used in C++ to represent something that needs a parameterizable type. This is used with static_cast to determine what data type the argument should be converted to (e.g. static_cast<int>(x) will convert x to an int).

A constant is a fixed value that may not be changed. C++ supports two types of constants: literal constants, and symbolic constants.

Literals are values inserted directly into the code. Literals have types, and literal suffixes can be used to change the type of a literal from default.

Const variables are variables that can’t be changed after being initialized. Const variables can be either runtime or compile-time constants.constexpr variables must be compile-time constants.

Don’t use magic numbers in your code. Instead, use symbolic constants.

Quiz time

Question #1

Why are symbolic constants usually a better choice than literal constants? Why are const/constexpr symbolic constants usually a better choice than #defined symbolic constants?

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Question #2

Pick the appropriate data type for a variable in each of the following situations. Be as specific as possible. If the answer is an integer, pick either int, long, or a specific fixed-width integer type (e.g. int16_t) based on range. If the variable should be const, say so.

a) The age of the user (in years)

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b) Whether the user wants color or not

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c) pi (3.14159265)

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d) The number of pages in a textbook (assume size is important)

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e) The length of a couch in feet, to 2 decimal places

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f) How many times you’ve blinked since you were born (note: answer is in the millions)

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g) A user selecting an option from a menu by letter

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h) The year someone was born (assuming size is important)

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Question #3

Author's note

The quizzes get more challenging starting here. These quizzes that ask you to write a program are designed to ensure you can integrate multiple concepts that have been presented throughout the lessons. You should be prepared to spend some time with these problems. If you’re new to programming, you shouldn’t expect to be able to answer these immediately.

Remember, the goal here is to help you pinpoint what you know, and which concepts you may need to spend additional time on. If you find yourself struggling a bit, that’s okay.

Here are some tips:

  • Don’t try to write the whole solution at once. Write one function, then test it to make sure it works as expected. Then proceed.
  • Use your debugger to help figure out where things are going wrong.
  • Go back and review the answers to quizzes from prior lessons in the chapter, as they’ll often contain similar concepts

If you are truly stuck, feel free to look at the solution, but take the time to make sure you understand what each line does before proceeding. As long as you leave understanding the concepts, it doesn’t matter so much whether you were able to get it yourself, or had to look at the solution before proceeding.

Write the following program: The user is asked to enter 2 floating point numbers (use doubles). The user is then asked to enter one of the following mathematical symbols: +, -, *, or /. The program computes the answer on the two numbers the user entered and prints the results. If the user enters an invalid symbol, the program should print nothing.

Example of program:

Enter a double value: 6.2
Enter a double value: 5
Enter one of the following: +, -, *, or /: *
6.2 * 5 is 31

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Show Hint

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Question #4

Extra credit: This one is a little more challenging.

Write a short program to simulate a ball being dropped off of a tower. To start, the user should be asked for the height of the tower in meters. Assume normal gravity (9.8 m/s2), and that the ball has no initial velocity (the ball is not moving to start). Have the program output the height of the ball above the ground after 0, 1, 2, 3, 4, and 5 seconds. The ball should not go underneath the ground (height 0).

Your program should include a header file named constants.h that includes a namespace called myConstants. In the myConstants namespace, define a symbolic constant to hold the value of gravity (9.8).

Use a function to calculate the height of the ball after x seconds. The function can calculate how far the ball has fallen after x seconds using the following formula: distance fallen = gravity_constant * x_seconds2 / 2

Sample output:

Enter the height of the tower in meters: 100
At 0 seconds, the ball is at height: 100 meters
At 1 seconds, the ball is at height: 95.1 meters
At 2 seconds, the ball is at height: 80.4 meters
At 3 seconds, the ball is at height: 55.9 meters
At 4 seconds, the ball is at height: 21.6 meters
At 5 seconds, the ball is on the ground.

Note: Depending on the height of the tower, the ball may not reach the ground in 5 seconds -- that’s okay. We’ll improve this program once we’ve covered loops.
Note: The ^ symbol isn’t an exponent in C++. Implement the formula using multiplication instead of exponentiation.

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5.1 -- Operator precedence and associativity
4.13 -- Const, constexpr, and symbolic constants

791 comments to 4.x — Chapter 4 summary and quiz

  • Gustav

    Hi Alex! Awesome tutorials, I'm having a blast doing these challenges.

    Could you please evaluate my code so I can improve it more, thanks!

    Unto the next chapters.

    • nascardriver

      Hi Gustav!

      - Initialize your variables with brace initialization (Line 14).
      - Use double literals for doubles (2.0 instead of 2, 0.0 instead of 0).
      - "calculateHeight" is a poor name for what the function does. If also reads and prints.
      - Inconsistent formatting. Use your editor's auto-formatting feature.
      - `fallen` should be declared inside of the loop. There's no extra cost to this, but it limits `fallen`'s scope.
      - Name your variables descriptively. `x` doesn't mean anything.

  • Strato

    Hi, thank you so much for this fantastic tutorial, here's my code for review. I didn't figure it out how to exit the main function if the ball get to the ground before the 5 seconds.

    • nascardriver


      - Avoid abbreviations
      - `constexpr` variables are always `inline`, you don't need to do it manually.
      - Use double literals for doubles (0.0 instead of 0, 2.0 instead of 2).
      - Line 9, 10: Duplicate call.

      > I didn't figure it out how to exit the main function if the ball get to the ground before the 5 seconds
      You could've used `if` and `return`, but that wouldn't look good. This quiz will come up later in the lessons about loops. You'll learn how to do it properly there.

  • knight

    Hi, Alex Thanks your tutorial, I understand your most lessons but when I encounter question 3 and 4 which I do not know how to code it. I don't remember many concepts. Could you add more questions or exercises at every lesson? That may help newer to enhance the concept.

  • Elis


    Managed to get a program working for Q#4 using a for loop, any feedback?
    On line 19 and 21 I got a warning for inserting an int with a smaller width into a larger one and was recommended to cast it, is this a reasonable way to do it?

    Thank you!



    • nascardriver

      Hi Elis!

      - Initialize your variables with brace initializers.
      - Limit your lines to 80 characters in length for better readability.
      - Line 10: There's no reason to use an int16.
      - Use double literals for doubles (2.0 instead of 2).
      - Line 17: `++seconds`.

      > On line 19 and 21 I got a warning
      The appropriate cast is to type `double`, as that's what you're using.

  • Alex

    This program is able to display the fly of the ball from whatever height till it reaches the ground using functions only.


    • Hi!

      - Name your variables and function descriptively, `a`, `elseFunction`, `s` are meaningless.
      - Initialize your variables instead of assigning to them.
      - Use double literals for doubles (2.0 instead of 2). Line 14 performs integer arithmetic.
      - `startOutput` and `elseFunction` are almost identical, they can be merged.
      - Inconsistent formatting. Use your editor's auto-formatting feature.

      You solved this quiz by using recursion (A function calling itself). This is discouraged, as it produces a big overhead (Wasted resources). You'll learn more about this and alternatives later. I think this quiz appears again in a different form, you'll have a head start :)

  • Adam

    • - Use ++prefix unless you need postfix++.
      - Use double literals for doubles (0.0 instead of 0, etc.).
      - Line 19 is missing parentheses. Your calculating `(time + time + 1)`.

      Line 19 can use `distancetoground -= /* ... */` to prevent the repetition of `distancetoground`.

  • Adam

    How is that?

  • Mike

    Quick suggestion, apologize if its already been suggested.

    Any chance of adding the chapter links from the main page to the side columns for all the pages? That way you can easily jump to a chapter for a quick refresher, which as a beginner happens too many times. You could easily click the chapter link, then just press back to return to where you were. Maybe even add the Previous, Index, and Next page to the top and/or very bottom of the page. This way you can just press Home or End to find them quickly.

    The search helps, though having a visual of the chapters only a click away would certainly facilitate user experience.

    • Alex

      I've gotten a similar request several times. Are you envisioning just a list of lesson numbers (0.1, 0.2, 0.3) that link to the respective lessons? Part of the challenge I have is that the sidebar isn't very wide, so the lesson names won't fit.

      • Mike

        Using my 17" and 22" monitors, it just seemed like there is a lot of empty space on both sides that could be put to good use. I don't think the lesson numbers by them self would help much as they would definitely need a description of some sort. I'm no web designer for sure, but what if you combine the blanks sides to just one side, moving the content of the page to the left or right? And when you say the lesson names won't fit, will they not wrap to the next line or is that just bad web design?

        • Alex

          I'm thinking maybe there's some overlay solution that might work (e.g. something you hover over that opens up a menu). I'll look into it, but probably not soon, as my focus is more on updating content right now.

          Thanks for the feedback!

  • Sri

    Please check any review my example:

    • - Initialize your variables with brace initializers.
      - Limit your lines to 80 characters in length for better readability.
      - Use double literals for doubles `2.0` instead of `2`. Same for `0`.
      - `main`: Missing `return`-statement.
      - You're using the same name style for variables and functions, this can lead to confusion.

  • Adriano

    Hi !
    First thank you so much for the time you spent on this tutorial, it's awesome.
    Second, i'd like to understeand something, i was looking at your file costant.h in the 4th quiz about the physic quest:


    i'm sorry but i don't understeand why all this , couldn't i declare constexpr double gravity in my "main file"? Wouldn't be easier and ok ?
    i know you asked it as a part of the quiz to test the knowledges of your students, but could i do that?
    And i'm sorry :
    #ifndef CONSTANTS_H
    #define CONSTANTS_H
    why do i need those delcarations?
    thank you so much sorry for my tricky question .

  • Jose

    Hi, I wrote this code for quiz 3 but I don´t know if it is possible to perform the calculation the way it is right now, is there a way to convert the operator character into a real operator in the "printResult()" function?

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