Introduction to Loops using C++. Exploring While&Do-While Loop

Understanding the basic concepts of Loops

1. Object Oriented Programming (Lab) Lecture 1-> LOOPS Semester- Spring 2024 Lahore Garrison University 1 Instructor name: Munawar Ahmad

2. How Many type of loops are in C++ ? Lahore Garrison University 2

3. Loops There are 3 types of loops in C++. for loop while loop do...while loop Lahore Garrison University 3

4. What is the difference between For and While Loop? Lahore Garrison University 4

5. for vs while loops Lahore Garrison University 5 A for loop is usually used when the number of iterations is known. For example, // This loop is iterated 5 times for (int i = 1; i <=5; ++ i ) { // body of the loop } Here, we know that the for-loop will be executed 5 times. However, while and do...while loops are usually used when the number of iterations is unknown. For example, while (condition) { // body of the loop }

6. C++ while C++ while Loop The syntax of the while loop is: while (condition) { // body of the loop } Lahore Garrison University 6 A while loop evaluates the condition If the condition evaluates to true, the code inside the while loop is executed. The condition is evaluated again. This process continues until the condition is false. When the condition evaluates to false, the loop terminates.

7. Flowchart of while Loop Lahore Garrison University 7

8. Example 1: Display Numbers from 1 to 5 Iteration Variable i <= 5 Action 1st i = 1 true 1 is printed and i is increased to 2. 2nd i = 2 true 2 is printed and i is increased to 3. 3rd i = 3 true 3 is printed and i is increased to 4 4th i = 4 true 4 is printed and i is increased to 5. 5th i = 5 true 5 is printed and i is increased to 6. 6th i = 6 false The loop is terminated Lahore Garrison University 8 #include <iostream> using namespace std; int main() { int i = 1; while ( i <= 5) { cout << i << " "; ++ i ; } return 0; }

9. Lahore Garrison University 9 Sum of Positive Numbers Only // program to find the sum of positive numbers // if the user enters a negative number, the loop ends // the negative number entered is not added to the sum #include <iostream> using namespace std; int main() { int number; int sum = 0; // take input from the user cout << "Enter a number: "; cin >> number; while (number >= 0) { // add all positive numbers sum += number; // take input again if the number is positive cout << "Enter a number: "; cin >> number; } // display the sum cout << "\n The sum is " << sum << endl ; return 0; } In this program, the user is prompted to enter a number, which is stored in the variable number. In order to store the sum of the numbers, we declare a variable sum and initialize it to the value of 0. The while loop continues until the user enters a negative number. During each iteration, the number entered by the user is added to the sum variable. When the user enters a negative number, the loop terminates. Finally, the total sum is displayed.

10. C++ do...while Loop Lahore Garrison University 10 The do...while loop is a variant of the while loop with one important difference: the body of do...while loop is executed once before the condition is checked. Its syntax is: do { // body of loop; } while (condition); The body of the loop is executed at first. Then the condition is evaluated. If the condition evaluates to true, the body of the loop inside the do statement is executed again. The condition is evaluated once again. If the condition evaluates to true, the body of the loop inside the do statement is executed again. This process continues until the condition evaluates to false. Then the loop stops.

11. Flowchart of do...while Loop Lahore Garrison University 11

12. Display Numbers from 1 to 5 Lahore Garrison University 12 // C++ Program to print numbers from 1 to 5 #include <iostream> using namespace std; int main() { int i = 1; // do...while loop from 1 to 5 do { cout << i << " "; ++ i ; } while ( i <= 5); return 0; } Iteration Variable i <= 5 Action i = 1 not checked 1 is printed and i is increased to 2 1st i = 2 true 2 is printed and i is increased to 3 2 nd i = 3 true 3 is printed and i is increased to 4 3 rd i = 4 true 4 is printed and i is increased to 5 4th i = 5 true 5 is printed and i is increased to 6 5th i = 6 false The loop is terminated

13. Lahore Garrison University 13 Sum of Positive Numbers Only // program to find the sum of positive numbers // If the user enters a negative number, the loop ends // the negative number entered is not added to the sum #include <iostream> using namespace std; int main() { int number = 0; int sum = 0; do { sum += number; // take input from the user cout << "Enter a number: "; cin >> number; } while (number >= 0); // display the sum cout << "\ nThe sum is " << sum << endl ; return 0; }

14. For Loop Lahore Garrison University 14 The syntax of for-loop is: for (initialization; condition; update) { // body of-loop } initialization – initializes variables and is executed only once condition – if true, the body of for loop is executed if false, the for loop is terminated update – updates the value of initialized variables and again checks the condition

15. Flowchart of for Loop in C++ Lahore Garrison University 15

16. Printing Numbers From 1 to 5 Lahore Garrison University 16 #include <iostream> using namespace std; int main() { for (int i = 1; i <= 5; ++ i ) { cout << i << " "; } return 0; }

17. Display a text 5 times Lahore Garrison University 17 // C++ Program to display a text 5 times #include <iostream> using namespace std; int main() { for (int i = 1; i <= 5; ++ i ) { cout << "Hello World! " << endl ; } return 0; }

18. Program to get the multiplication table of a given number in the m*n format using nested for loop . #include <iostream> int main () { using namespace std; int m; int n; for (m = 10; m <= 11; m++) { cout << "Table of " << m << endl ; for (n = 1; n <= 10; n++) {cout << m << "*" << n << "=" << (m*n) << endl ;} } return 0; } Lahore Garrison University 18

19. Sum of Positive Numbers Only by using break #include <iostream> using namespace std; int main() { int number = 0, sum = 0; for (;;) { // take input from the user cout << "Enter a number: "; cin >> number; // exit loop if number is negative if (number < 0) { break; } sum += number; } // display the sum cout << "\ nThe sum is " << sum << endl ; return 0; } Lahore Garrison University 19

20. Sum of Positive Numbers (Only lesser than 50) by using For Loop with Continue // program to calculate positive numbers till 50 only // if the user enters a negative number, // that number is skipped from the calculation // negative number -> loop terminate // numbers above 50 -> skip iteration #include <iostream> using namespace std; int main() { int sum = 0; int number = 0; while (number >= 0) { // add all positive numbers sum += number; // take input from the user cout << "Enter a number: "; cin >> number; // continue condition if (number > 50) { cout << "The number is greater than 50 and won't be calculated." << endl ; number = 0; // the value of number is made 0 again continue; } } // display the sum cout << "The sum is " << sum << endl ; return 0; } Lahore Garrison University 20

21. Write a program in C++ to find the sum of the series 1 + 1/2^2 + 1/3^3 + …..+ 1/ n^n . #include <iostream> #include < math.h > using namespace std; int main() { double sum = 0, a; int n, i ; cout << " Input the value for nth term: "; cin >> n; for ( i = 1; i <= n; ++ i ) {a = 1 / pow( i , i ); cout << "1/" << i << "^" << i << " = " << a << endl ; sum += a; } cout << " The sum of the above series is: " << sum << endl ; } Lahore Garrison University 21

22. Home Task Write a program that uses nested for loop to find the prime numbers from 1 to 100. Write a program that uses a for loop to print out the numbers from 1 to 100. For every number that is divisible by 3, print "Fizz" instead of the number. For every number that is divisible by 5, print "Buzz" instead of the number. For every number that is divisible by both 3 and 5, print "Fizz Buzz" instead of the number. Write a program that asks the user to enter a number, and then uses a while loop to print out the multiplication table for that number, from 1 to 10. Write a program that asks the user to enter a password, and then uses a do-while loop to keep asking for the password until the correct password is entered. Write a program that asks the user to enter a positive integer, and then uses a do-while loop to keep asking for a number until the user enters a number that is divisible by 3. Lahore Garrison University 22