While loops

We use loops in programming to repeat execution of a block of code instead of repeating the entire code. In C ++ we have 3 types of loops: - for-loops - while loops - do-while loops.

The execution of a loop can be controlled using the following keywords - break - terminates the loop (or switch) -statement and transfers execution to the statement directly after the loop - continue - will cause the loop to process to the next element skipping the current one - goto LABEL - transferes control to the specified label. IT IS NOT ADVISED TO USE THIS STATEMENT!

"while" loop

A "while" loop will repeat a statement or a group of statements while a given condition is true.

Examples:

//Guessing game
#include <iostream> 
using namespace std; 
int main (void) 
{     
    int searched = 5;  //The value we're searching
    int given = -1; // The variable to which we'll write user's guesses

    //Greet the user:
    cout << "This is simple guessing game:" << endl;
    cout << "Please enter a number:" << endl;

    //This while-loop will terminate when the user entered the searched value
    while (searched != given) {
        cin >> given;  // Read a value from the keyboard

        /*
        Note, that the following line(s) within the loop-brackets
        will also execute if the user guessed correctly.
        Checking will be done at the start of the next iteration
        */

        cout << "Thank you for your guess..." << endl;  
    }
cout << "You found the correct number. Good bye." << endl;
return 0;
}

// Some while with continue- and break-statements
#include <iostream> 
using namespace std; 
int main (void) 
{     
    int count = 200;  // The start value
    int destination = 0;  // the destination

    // This while will normally terminate when count reaches the destination-value
    while (count > destination) {  
        count--;  // decrement count

        if (count == 190) { // If count will turn into 190...
            cout << "skipped..." << endl;
            continue; //... the while-loop will skip to the next iteration due to the "continue"-statement.
        }

        if (count < 180) { // If count falls below 180...
            cout << "aborted..." << endl;
            break; //... the while-loop will be aborted due to the "abort"-statement.
        }
        cout << count << endl;  //Note, that this will also execute when target is reached
    }

return 0;
}

Exercise

Try to print all the numbers from 1 to 20 in ascending order using a while loop.