The structure of the Do While Loop

Below is the structure:

do { 

//statements 

} while ( condition(s) ) ;

What is this useful for? In order to execute a set of commands at least once.

Introducing the While Loop

The structure is below.

while ( condition ) {

statements to be executed

}

Let’s make a guessing game where the user guesses a number and the user continues with the program until he guesses the correct number.

int guess;
int numberToGuess = 27;
cin >> guess;

while ( guess != numberToGuess ) {
cout << "Sorry! Wrong number.\nKeep Guessing!\n";
}

cout << "Congratulations you guessed the correct number!\n";

How it the While Loop works

It’s straightforward actually. It simply continues executing the statements until the condition is met. It’s very similar to the if statements. You can have multiple conditions to be satisfied in order for the program to break out of the while loop. An example is below.

int num1 = 25;
int num2 = 75;

int guess;

cout << "Pick a number between our mystery two numbers!";

cin >> guess;

while ( num1 < guess && num2 > guess  ) {
cin >> guess;
}

cout << "Congratulations you picked the correct range for your number!\n";

Further Practice with While Loops

Exercise 1: Make the user guess a magic number. Tell them if their number was either below or above the one they guess.

Exercise 2: Make the user guess a magic number. If they got it correct. Make them guess a second magic number. If they don’t get it right the first time, they start again!

*Hint: You can do it with 2 while loops.

Challenge 1: Determine if a word is a palindrome. What is a palindrome? mom, racecar, dad…

*Hint: Something found here will help you out solve this problem!

The Foor Loop

How would you calculate the factorial of 1-10 without using loops? Below would be one of many solutions.

int factorial = 1;
cout << "!1 = " << factorial << endl;
factorial = factorial * 2;
cout << "!2 = " << factorial << endl;
factorial = factorial * 3;
cout << "!3 = " << factorial << endl;
factorial = factorial * 4;
cout << "!4 = " << factorial << endl;
factorial = factorial * 5;
cout << "!5 = " << factorial << endl;
//Ok! That's a lot of work!

Would print out

!1 = 1
!2 = 2
!3 = 6
!4 = 24
!5 = 120

Imagine doing this simple operation up to 100.

Structure of the for loop

Below is the structure of a for loop.

for ( initialization of variable(s) ; condition ; assignment of different value to the previous value )
{
     statements to be executed
}

Don't worry if you don't understand, below you'll see an example.

Below is a "for loop" that will perform the same operation and can be easily manipulated to perform the previous operations from 1-10 and even to 100 with simple ease.

int number = 10;
int factorial = 1;
for ( int i = 1; i <= number; i++ )
{
     //Multiplies the previous factorial value by the index value to calculate the next factorial
     factorial = factorial*i;
     cout << "!" << i << " = " << factorial << endl;
}

Breaking down the For Loop

Below is a detailed explanation of how the previous code works.

int number = 10; //We want to display !1 - !10 Change this number, to go even further!

int factorial = 1; //This will be the integer that keeps track of the previous factorial value to be able to find the next with ease

for ( int i = 1; i <= number; i++ ) //Below is the break down

//This variable pertains to this for loop and will reach out of scope once the loop finishes executing. This variable can be though of an index. Since we are finding the values of the factorial in increments of one, its obvious to start with 1.
int i = 1; 

//This is the condition in which this loop will execute until it is no longer true. Our number is 10, so while our index value is less than our number, this loop will execute.
i <= number 

//This increments our index value by 1 so we can cover all numbers from 1-10. We can also use statements such as (i += 2) , ( i-- ) , ( i *= 2 ) , and more.
i++

Let's break this down, this for loop executes these lines of code.

int factorial = 1;
int i = 1;
factorial = factorial * i; // !1 = 1 * 1 = 1
i++; //i = 2;
factorial = factorial * i;// !2 = 2 * 1 = 2
i++; //i = 3;
factorial = factorial * i;// !3 = 3 * 2 = 6
//and so on...until our condition is met

How to master For Loops

With practice! Write down the steps taken. Try to change the values of the variables to see what happens.



Some examples to try out can be the following.

Example 1: Counting from 1 to 100

 1 2 3 4 5 6 7 8 9 10 11 ...

Example 2: Counting from 100 to 1

 100 99 98 97...

Example 3: The classic Triangle of Stars

 ****
***
**
*

*Hint You will need to use two for loops instead of one. Can you figure out how? Need help? Visit the Forums. Registration is free, and you can ask your questions and get answers!