In C++ programming language, the repetitive operation is done through loop control instruction. There are three methods by which we can repeat a part of a program. 

Types of Loops:

• Entry Controlled Loops: The test condition is tested before entering the loop body in this type of loop. Entry-controlled loops are For Loop and While Loop.
• Exit Controlled Loops: The test condition is tested or evaluated at the end of the loop body in this type of loop. As a result, regardless of whether the test condition is true or false, the loop body will execute at least once. The do-while loop is a loop that is exit controlled.

for Loop:

The for loop lets us specify three aspects of a loop in a single line:

• Initialization: Setting the loop counter to a starting value.
• Condition: Checking the loop counter to see if it has reached the desired number of repetitions.
• Updating: Increasing the value of the loop counter after each execution of the program segment within the loop.

Syntax:

for(initialization ; condition ; updation)
{ 
    //statement1
    //statement2
}

Example: Table of 5

#include <iostream>
using namespace std;

int main()
{
	for (int i = 1; i <= 10; i++)
	{
		cout << 5*i<<"\n";
	}

	return 0;
}

Output:

5
10
15
20
25
30
35
40
45
50

Nested for loop:

Just like nested if-else, we can make use of nested for loop as per our requirement.

Syntax:

for(initialization; condition; increment/decrement)
{
    for(initialization; condition; increment/decrement)
    {
        statement;
    }
}

while loop:

In C++, the while loop is an entry-controlled loop (Entry Controlled Loops are used when checking a test condition is mandatory before executing the loop body). It is typically used when the number of iterations is unknown.

Syntax:

initialization;
while(condition)
{
   //code to be executed
   updation;
}

Example:

#include <iostream>
using namespace std;

int main()
{
	// initialization expression
	int i = 1;

	// test expression
	while (i < 6)
	{
		cout <<i <<"\n";

		// update expression
		i++;
	}

	return 0;
}

Output:

1
2
3
4
5

do-while loop:

The do-while loop in C++ is an exit-controlled loop; unlike the for and while loops, the condition is checked at the end of the loop (i.e., after all the statements inside the do-while block have been executed), so the do-while loop runs at least once in the program even if the condition fails.

syntax:

do
{
  //statements to be executed
}while(condition);

Example:

#include <iostream>
using namespace std;

int main()
{
	int i = 2; // Initialization expression

	do
	{
		// loop body
		cout << i<<"\n";

		// update expression
		i=i+2;

	} while (i < 11); // test expression

	return 0;
}

Output:

2
4
6
8
10

Note: also read about the Decision-Making in C++

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