Iteration Statements

Loops

Entry Controlled

for loop

The for loop is used when the number of iterations is known in advance. It consists of three parts: initialization, condition, and iteration.

Fig. 1 for loop

// Syntax

for (initialization; condition; iteration) {
    // Code block to be executed repeatedly
}

// Example

// C++ program to illustrate If statement
#include <iostream>
using namespace std;

int main()
{

  for (int i = 0; i < 5; i++) {
      cout << i << endl;
  }

}

// Output

0
1
2
3
4

The loop initializes the variable i to 0, checks the condition i < 5, executes the code block, increments i by 1, and repeats the process until the condition is no longer true.

while loop

The while loop is used when the number of iterations is not known in advance. It repeats a block of code as long as a specified condition is true.

Fig. 2 while loop

// Syntax

while (condition) {
    // Code block to be executed repeatedly
    // Condition should eventually become false to exit the loop
}

// Example

// C++ program to illustrate If statement
#include <iostream>
using namespace std;

int main()
{

  int i = 0;
  while (i < 5) {
      cout << i << endl;
      i++;
  }

}

// Output

0
1
2
3
4

The loop checks the condition i < 5 before each iteration. If the condition is true, it executes the code block, increments i by 1, and repeats the process until the condition becomes false.

Exit Controlled

do while

The do-while loop is similar to the while loop, but it guarantees that the code block is executed at least once before checking the condition.

Fig. 3 do-while loop

// Syntax

do {
    // Code block to be executed repeatedly
    // Condition should eventually become false to exit the loop
} while (condition);

// Example

// C++ program to illustrate If statement
#include <iostream>
using namespace std;

int main()
{

  int i = 0;
  do {
      cout << i << endl;
      i++;
  } while (i < 5);

}

// Output

0
1
2
3
4

The loop executes the code block at least once because the condition i < 5 is checked after the first iteration. If the condition is true, it repeats the process until the condition becomes false.