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 by 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.

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 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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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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O.3.1 -- Operator precedence and associativity
4.13 -- Const, constexpr, and symbolic constants

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

  • Torraturd

    Is it okay if I answer the question like this?

    • * Initialize your variables with brace initializers.
      * Line 8, 28: Limit your lines to 80 characters in length for better readability on small displays.
      * Use double literals for doubles (0.0 instead of 0, 2.0 instead of 2, etc.).
      * Use @std::pow instead of @pow
      * Missing #include <cmath>
      * Line 22+: Should be a do-while-loop.
      * Name your variables descriptively.

  • Richard Flores

    For Q3 can I use a switch case instead?
       switch (opr) {
          case '+' :
             totalVal = val1 + val2;
          case '-' :
             totalVal = val1 - val2;
          case '*' :
             totalVal = val1 * val2;
          case '/' :
             totalVal = val1 / val2;
          default :
             isValid = 0;

    Are operator chars allowed in case inputs or must they be integers only?

  • Jonathan

    Maybe I will change the code to loops if I learn it. What can be improved in the code?

  • Cal

    You've got a typo "poitners" in the data types part of the quick review up top.

  • Napalm

    Question 4



    I'm proud to have finally got this to work without cheating! It turned out different to the answer though. I think I may have broken the one job function rule though, it looks like I got the use of printResult() and distanceFallen a bit jumbled. The only other issue was that it keeps printing "the ball is on the ground" rather than stopping.

    Is it bad practice to put "using namespace" for this?

    Any more feedback would be great.

    • main.cpp
      * Line 20: Initialize your variables with brace initializers.
      * Line 20: Re-assigning to @t is unnecessary. Use a simple multiplication.
      * Line 26: Use double literals for doubles (0.0 instead of 0).
      * Line 29: Limit your lines to 80 characters in length for better readability on small displays.
      * "g", "h", "t" are useless names. Name variables descriptively, avoid abbreviations.
      * Line 40, 42, 44, 46, 48: Should be ++time to prevent human error.
      * @main: Missing return-statement.

      > Is it bad practice to put "using namespace" for this?
      It'd be better without it. That way it's obvious where @gravity is coming from and name collisions are prevented. As long as the using-statement is in a source file and you know the contents of the namespace, you _can_ use "using namespace", but you should do so with care.

  • p1n

    Hey can i get help with this program.When i enter integer numbers it works,but with float it doesn't. I tried answering the third question like this.



    Thanks in advance.
    I'm an idiot,I always typed comma instead of a dot while typing float numbers.
    I still wonder is this better than the solution showed.

  • Avijit Pandey

    I attempted question number 4, and here's my solution:

    So, i noticed that mine is considerably shorter than yours, what i want to know is if it is a good practice to keep your code as comapct as possible or not, additionally, if i made any novice mistakes that i am not noticing since its not causing any problems as of yet.

    • * Line 6: Use double literals when calculating with doubles (2.0 instead of 2).
      * Line 10, 13: Limit your lines to 80 characters in length for better readability on small displays.
      * Inconsistent formatting. Use your editor's auto-formatting feature.

      > is a good practice to keep your code as comapct as possible
      No. Compact code is often harder to read and less reusable. You cannot calculate the height at a given time without printing it. Alex can.

  • Hi Alex!

    Q2 encourages the use of of types (@std::int16_t) that were previously warned about (Lesson 4.6).

  • Louis Cloete

    Hint #2 at Q3: should be operator== (equality comparison, not assignment)?

  • Louis Cloete

    I don't understand Quiz Q2 e-g. What is the question asking?

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