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Object Oriented
Programming (Lab)
Lecture 1-> LOOPS
Semester- Spring 2024
LAHORE GARRISON UNIVERSITY
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Instructor name: Munawar Ahmad

 How Many type of loops are in C++ ?
Lahore Garrison University
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Loops
There are 3 types of loops in C++.
 for loop
 while loop
 do...while loop
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 What is the difference between For and While Loop?
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for vs while loops
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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
}

C++ while
C++ while Loop
The syntax of the while loop is:
while (condition) {
// body of the loop
}
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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.

Flowchart of while Loop
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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 falseThe loop is terminated
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#include <iostream>
using namespace std;
int main() {
int i = 1;
while (i <= 5) {
cout << i << " ";
++i;
}
return 0;
}

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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>
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
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.

C++ do...while Loop
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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.

Flowchart of do...while Loop
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Display Numbers from 1 to 5
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// C++ Program to print numbers from
1 to 5
#include <iostream>
int main() {
int i = 1;
// do...while loop from 1 to 5
do {
cout << i << " ";
++i;
}
while (i <= 5);
return 0;
}
Iteration Variablei <= 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
2nd i = 3 true 3 is printed and i is increased to 4
3rd 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

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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>
int main() {
int number = 0;
int sum = 0;
do {
sum += number;
// take input from the user
cin >> number;
}
while (number >= 0);
// display the sum
cout << "nThe sum is " << sum << endl;
return 0;
}

For Loop
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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

Flowchart of for Loop in C++
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Printing Numbers From 1 to 5
Lahore Garrison
University
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#include <iostream>
int main() {
for (int i = 1; i <= 5; ++i) {
cout << i << " ";
}
return 0;
}

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

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
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Sum of Positive Numbers Only by using
break
 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;
 }
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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
 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;
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Write a program in C++ to find the sum of the
series 1 + 1/2^2 + 1/3^3 + …..+ 1/n^n.
 #include <math.h>
 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;
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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.
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