Do While Loop

The syntax for the Do While Loop is below:

do { 
 
// Statements ...
 
} while ( condition );

Do While Example

An example of a do while loop is below.

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string msg;
 
do { 
   cout << "Enter a word or 'exit' to quit: " << endl;
 
   cin >> msg;
} while ( msg != "exit" );

Do While Loops aren’t used as extensively as While Loops and For Loops in practice due to their nature. They are only used for specific cases where the programmer needs the block of statements to be executed at least once.

Going further with Do While Loops

Now that you understand Do While Loops, While Loops, and For Loops why not try the following?

1. Create a factorial program that uses a while, do while, and for loop. Do the same for summation. This should make you fully understand all loops and when to use them.

Example of Control Flow

Boolean Comparison Operators

Before we teach you how to write these statements, we’ll show you the boolean comparison operators you may use for creating conditions. These condition statements will return either TRUE or FALSE which are useful in if statements.

Operator	Example	Description
>	a > b, a > 2, 4 > 2	Greater than
>=	a >=b, a >= 2, 4 >= 2	Greater than or equal to
<	a < b, a < 2, 4 < 2	Less than
<=	a <= b, a <=2, 4 <= 2	Less than or equal to
==	a == b, 2 == a	Equal to
!=	a != b, 2 != a	Does Not Equal to

You may use these boolean operators to compare data types of similar type. You may compare any of the C++ Data Types with each others whether they are literals such as 2, 3, “Hello”, or variables. If you compare mixed data types you will get different behavior.

Below are some examples of conditions. If they are literals, determine the conditions truth value.

2 < number
 
"Hello" == "HELLO"
 
'a' != 'A'
 
2.0 == 2

You may also use the && (and) and || (or) connectives in order to have multiple conditions. Below is an everyday example and after that some C++ examples.

 
// Returns true if both the 1st and 2nd conditions are true
2 < a && b > c
 
// Returns true if either the 1st or 2nd conditions are true
2 < a || b > c

Finally, you may also use the ! connective to make a condition have the opposite truth value. An example is below:

int a, b;
a = 2;
b = 3;
 
// The following would return TRUE
a < b 
 
// The following would return FALSE because the ! 
// negates the truth value between the parenthesis
! ( a < b )

C++ If Statement

We will now start by showing you the syntax for writing an if statement.

if ( condition ) { 

statements ...

}

Now, we’ll actually put it to some use. In our previous tutorial we learned about user input which will help us make things a lot more interesting. Let’s say we wanted to create a program that asks the user to guess a number and we’ll simply reply if it was the correct one. We’d do it in the following manner.

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int magicNumber = 27;
 
int guess;
 
cout << "Guess my magic number: ";
 
cin >> guess;
 
if ( magicNumber == guess ) {
     cout << "Congratulations! Correct guess!" << endl;
}

In the code above, the statement inside the if clause would execute if the condition were true. Therefore, if the user chooses our magic number 27, our program will congratulate the user.

If Statement Diagram

C++ If Else Statement

Well, what if they didn’t? We would want to give them another message saying it was incorrect. Your first guess might be making another if statement but we can use the else statement.

if ( condition ) { 

statements ...

} else { 

statements ...

}

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// .. Previous code
 
if ( magicNumber == guess ) {
     cout << "Congratulations! Correct guess!" << endl;
} else { 
    cout << "Incorrect!" << endl;
}

In the previous code, if the user guess the number correctly, the program would congratulate the user. If the user did not guess the number correctly, it would display Incorrect!

If Else Statement

C++ If Else If Else Statement

Now, what if we wanted to actually let them know if their guess was too high or too low if it was incorrect? We can then use the else if statements.

if ( condition ) { 

statements ...

} else if ( condition ) { 

statements ...

} else { 

statements ...

}

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// .. Previous code
 
if ( magicNumber == guess ) {
     cout << "Congratulations! Correct guess!" << endl;
} else if ( magicNumber > guess ) {
    cout << "Your guess is too low!" << endl;
} else {
    cout << "Your guess is too high!" << endl;
}

If Else Else If Statements

Nesting If Statements

You may also have nest if statements within if statements. An example is below.

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cin >> guess;
number = 25;
 
if ( number == guess ) {
 
     cout << "Now try guessing the second number!\n";
     // Guess a second number
     number = 56;
     cin >> guess;
 
     if ( number == guess ) { 
         cout << "Congratulations! You guess two numbers correctly!\n";
     } else { 
         cout << "Try next time!\n";
     }
} else { 
    cout << "Incorrect!\n";
}

Overview of If Statements

Some things to know about if statements are mentioned below.

1. Remember, the else statement is optional and you may have zero, one, or more else if statements.
2. For good practice always indent or more formally known as tab your code when its within an if statement. That way it’s easy to follow. Imagine going over nested if statements that don’t have tabs? You would have a hard time figuring out which statements belong where.

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   if ( a > b ) { if ( c < 2 ) { cout << "Yes!"; } else { cout << "No!"; } } else { cout << "What?"; }

3. If you only have one statement within an if statement you may omit the {}’s. For good practice, just keep them. It’s easier for someone else to go back to read and add to your code.

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   if ( a == b ) { cout << "Yes!"; }   // Is the same as   if ( a == b ) cout << "Yes!";

Going further with If Statement

Now that you know the basics of If Statements, why not do the following?

1. Create an if statement that contains a condition that is always true.
2. Are “Hello” and “HELLO” equivalent? What about the char ‘a’ and a string “a”?
3. Create a 3rd level deep if statement. The previous example shown was nested 2x.

Keep patient, in our next tutorial we will learn about for loops and then while loops. Once we get a good handle of control flow, we can make some interesting programs.

The Switch Statement

The structure of a switch statement is the following:

 switch(expression) {
    case   :
    statements
    break;

    case  :
    statements
    break;

    //More cases...

    default :
    statements
}

The case to be executed is determined based on the value of the constant_expression. In other words, you may have an int, char, etc…They must be constants. The break statement once encountered breaks out of the switch statement. In other words, if you don’t include the break statement in one of your cases, it will simply execute the following cases until it reaches a break or the end of switch statement. The default case is simply all other cases not covered.

An example would be…

 cin >> number;
switch(number) {
     case 1:
     cout << "One\n";
     break;
     case 2:
     case 3:
     cout << "My favorite numbers...\n";
     break;
     default:
     cout << "What!?\n";
}

In other words, if the user chooses 1, they will encounter case 1, if they choose 2 or 3, they receive "My favorite..." statement, else they receive "What!?".

Another example comparing an if else statement with a switch statement

Imagine a banking program in which the teller gives the program an integer value to perform a different action. Each action determines the reward the user receives.

1 - Gold Reward... Receives $100 reward plus all the other rewards
2 - Silver Reward... Received $50 reward plus the Bronze Reward
3 - Bronze Reward... Received $25 reward
* - Deduct $100 from their account

*Denotes any other value

How would this look like with a if and else statement?

cin >> action;

if ( action == 1 ) {
     //Give Gold Award
     //Give Silver Reward
     //Give Bronze Reward }
else if ( action == 2 ) {
     //Give Silver Reward
     //Give Bronze Reward }
else if ( action == 3 ) {
     //Give Bronze Reward }
else {
     //Deduct $100 from their account }
}

What about with a switch statement?

 cin >> action;

switch(action) {
     case 1:
     //Give Gold Reward
     case 2:
     //Give Silver Reward
     case 3:
     //Give Bronze Reward
     break;
     default:
     //Deduct $100 from their account
}

In other words, once action satisfies one case, it keeps executing the statements until it reaches the break statement which breaks out of the switch statement. Wouldn't this be much easier to for a reader to understand? Most likely in certain cases.

The If Statement

An example is as follows

int x;
if ( condition ) x = 50; //If condition returns TRUE, assign 50 to X.

In other words, if the condition you provide returns a boolean value ( is a value that returns either TRUE or FALSE ) TRUE, then the following statements enclosed with {}’s are executed (no need if only one statement follows the if statement).


You may use the following operands in your conditions…
== – EQUAL TO
!= – NOT EQUAL TO
< - LESS THAN
<= - LESS THAN OR EQUAL TO
> – GREATER THAN
>= – GREATER THAN OR EQUAL TO

Here is an actual example.

int number;
cin >> number;
if ( number == 50 ) {
cout << "Congratulations! You picked the right number!" << endl;
}

In other words, if the user typed in 50, the if statement will be true and print the following line to the screen.

The If and Else

Let's say we want to output something if it was false.

int number;
cin >> number;
if ( number == 50 ) {
cout << "Congratulations! You picked the right number!" << endl;
}
else {
cout << "Sorry! You were wrong!" << endl; //Second Statement
}

Then, if the user didn't type in 50, it would output the second statement.

The If, Else-If, and Else

What if we wanted to check other conditions as well?

int number;
cin >> number;
if ( number == 50 ) {
cout << "Congratulations! You picked the right number!" << endl;
}
else if ( number > 50 ) {
cout << "Sorry! You were over!" << endl; //New Statement
}
else {
cout << "Sorry! You were way off!" << endl;
}

In other words, this one has a different output if the user entered a number larger than 50! If the user didn't choose 50, or a number larger than fifty, then the last else statement would be executed.


Keep in mind that you may add multiple else if statements! Just remember to have good coding style in order for any future reader to understand what statements pertain to what if condition. The way my code is written is a really good way of styling your code as its easy to read and follow!

So what now?

If you have trouble don't be afraid to post below any questions, comments, or concerns!

In the next tutorial expect to learn how to use If, Else If, and Else statements in more detail!