how to apple while,for and do loops in C++

1. Loop constructs

2. 2
Loops
• Loops cause a section of your program
to be repeated a certain number of
times
• Repeats until the condition remains true
• Terminates when the condition becomes
false

3. 3
Loops in C++
1. for loop
2. while loop
3. do loop

4. 4
(1) for loop - Syntax
for (int j=0; j<10; j++)
cout << j * j <<endl;
Initialization
expression
Test Condition
Increment expression
cout << j*2 <<endl;
cout << j*j*j <<endl;

5. 5
The general format for a for loop
for (Initialization_action; Condition; Condition_update)
{
statement_list;
}
int n,f=1;
cin >> n;
for (i=2; i<=n; i++)
{
f *= i;
}
cout << “The factorial of ” << n << “ is ” << f << “.”;
1 2 3
Factorial of n is n(n-1)(n-2)...21

6. 2-while loop
• for loop does something a fixed number of times.
• If you don’t know how many times you want to do
something before you start the loop?
• In this case a different kind of loop may be used:
the while loop

7. 7
while
Condition
Statement
list
T
F
while (Condition)
{
Statement list
}

8. while loop - syntax
Loop body contain
single statement
Loop body contain
Multiple statement

9. 3-do loop
• In while loop if condition is false it is never entered
or executed
• Sometime, requirements are that the loop should
be executed at least once….
• For that, we use do loop, that guarantees at least
on execution of the loop body

10. do while loop - syntax
Loop body contain
single statement
Loop body contain
Multiple statement

11. 11
do-while
Condition
Statement
list
T
F
do
{
Statement list
} while (Condition);
string ans = “n”;
while (ans != “Y”)
{
cout << “Would you marry me?”;
cin >> ans;
}
cout << “Great!!”;
; is required
do
{
cout << “Would you marry me?”;
cin >> ans;
} while (ans != “Y”);
cout << “Great!!”;

12. Conclusion
C++ provides three different loops for
eliciting repetitive behavior.
Which one is best to solve a given
problem depends on the algorithm for
that problem.