Loops in C++ allow programmers to repeatedly execute a block of code. There are three main types of loops in C++: while loops, do-while loops, and for loops. While loops and do-while loops check the loop condition at the end of each iteration and repeat the block while the condition is true. For loops allow initialization of a counter variable, a condition to test on each pass, and an update to the counter. For loops are useful when the number of iterations is known. Do-while loops differ in that the block is guaranteed to run at least once even if the condition is false.

1. C++ Loops
What are Loops in C++?
There may arise some situations during programming where programmers
need to execute a block of code several times (with slight variations
sometimes). In general, statements get executed sequentially with a C++
program, one statement followed by another. C++ provides statements for
several control structures along with iteration/repetition capability that allows
programmers to execute a statement or group of statements multiple times.
C++ supports following types of loops:
 while loops
 do while loops
 for loops
All are slightly different and provides loops for different situations.
Figure - Flowchart of Looping:

2. FOR - for loops are the most useful type. The syntax for a for loop is
for ( variable initialization; condition; variable update ) {
Code to execute while the condition is true
}
The variable initialization allows you to either declare a variable and give it a
value or give a value to an already existing variable. Second, the condition
tells the program that while the conditional expression is true the loop should
continue to repeat itself. The variable update section is the easiest way for a
for loop to handle changing of the variable. It is possible to do things like x++,
x = x + 10, or even x = random ( 5 ), and if you really wanted to, you could
call other functions that do nothing to the variable but still have a useful effect
on the code. Notice that a semicolon separates each of these sections, that
is important. Also note that every single one of the sections may be empty,
though the semicolons still have to be there. If the condition is empty, it is
evaluated as true and the loop will repeat until something else stops it.

3. void main()
{
for (i = 1; i <= 10; i++)
{
Cout<< "Hello Worldn";
}
}
While Loop
While studying for loop we have seen that the number of iterations is
known beforehand, i.e. the number of times the loop body is needed to be
executed is known to us. while loops are used in situations where we do
not know the exact number of iterations of loop beforehand. The loop
execution is terminated on the basis of test condition.
Syntax:
We have already stated that a loop is mainly consisted of three statements
– initialization expression, test expression, update expression. The syntax
of the three loops – For, while and do while mainly differs on the placement
of these three statements.
initialization expression;
while (test_expression)
{
// statements
update_expression;
}
void main()
{
// initialization expression
int i = 1;

4. // test expression
while (i < 6)
{
printf( "Hello Worldn");
// update expression
i++;
}
}
do while loop
In do while loops also the loop execution is terminated on the basis of test
condition. The main difference between do while loop and while loop is in
do while loop the condition is tested at the end of loop body, i.e do while
loop is exit controlled whereas the other two loops are entry controlled
loops.
Note: In do while loop the loop body will execute at least once irrespective
of test condition.
Syntax:
initialization expression;
do
{
// statements
update_expression;
} while (test_expression);
void main()
{
int i = 2; // Initialization expression
do
{

5. // loop body
cout << "Hello Worldn";
// update expression
i++;
} while (i < 1); // test expression
}