C++ for loop

C++ Tutorial

C++ Introduction

• C++ Variables and Literals
• C++ Data Types
• C++ Basic I/O
• C++ Type Conversion
• C++ Operators
• C++ Comments

C++ Flow Control

• C++ if…else
• C++ for Loop
• C++ do…while Loop
• C++ break & continue
• C++ switch Statement
• C++ goto Statement

C++ Functions

• C++ Functions
• C++ Function Types
• C++ Function Overloading
• C++ Default Argument
• C++ Storage Class
• C++ Recursion

C++ Arrays & String

• C++ Arrays
• Multidimensional Arrays
• C++ Function and Array
• C++ String

C++ Structures

• C++ Structure
• Structure and Function
• C++ Pointers to Structure
• C++ Enumeration

C++ Object & Class

• C++ Objects and Class
• C++ Constructors
• C++ Objects & Function
• C++ Operator Overloading

C++ Pointers

• C++ Pointer
• C++ Pointers and Arrays
• C++ Pointers and Functions

C++ Inheritance

• C++ Inheritance
• Inheritance Access Control
• C++ Function Overriding
• Multiple & Multilevel Inheritance
• C++ Friend Function
• C++ Virtual Function

In this tutorial, we will learn about the C++ for loop and its working with the help of some examples.

In computer programming, loops are used to repeat a block of code.

For example, let’s say we want to show a message 100 times. Then instead of writing the print statement 100 times, we can use a loop.

That was just a simple example; we can achieve much more efficiency and sophistication in our programs by making effective use of loops.

There are 3 types of loops in C++.

• for loop
• while loop
• do...while loop

This tutorial focuses on C++ for loop. We will learn about the other type of loops in the upcoming tutorials.

---

C++ for loop

The syntax of for-loop is:

for (initialization; condition; update) {
    // body of-loop 
}

Here,

• 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

To learn more about conditions, check out our tutorial on C++ Relational and Logical Operators.

---

Flowchart of for Loop in C++

Flowchart of for loop in C++

---

Example 1: Printing Numbers From 1 to 5

#include <iostream>

using namespace std;

int main() {
        for (int i = 1; i <= 5; ++i) {
        cout << i << " ";
    }
    return 0;
}

Output

1 2 3 4 5

Here is how this program works

Iteration	Variable	i <= 5	Action
1st	i = 1	true	1 is printed. i is increased to 2.
2nd	i = 2	true	2 is printed. i is increased to 3.
3rd	i = 3	true	3 is printed. i is increased to 4.
4th	i = 4	true	4 is printed. i is increased to 5.
5th	i = 5	true	5 is printed. i is increased to 6.
6th	i = 6	false	The loop is terminated

---

Example 2: Display a text 5 times

// C++ Program to display a text 5 times

#include <iostream>

using namespace std;

int main() {
    for (int i = 1; i <= 5; ++i) {
        cout <<  "Hello World! " << endl;
    }
    return 0;
}

Output

Hello World!
Hello World!
Hello World!
Hello World!
Hello World!

Here is how this program works

Iteration	Variable	i <= 5	Action
1st	i = 1	true	Hello World! is printed and i is increased to 2.
2nd	i = 2	true	Hello World! is printed and i is increased to 3.
3rd	i = 3	true	Hello World! is printed and i is increased to 4.
4th	i = 4	true	Hello World! is printed and i is increased to 5.
5th	i = 5	true	Hello World! is printed and i is increased to 6.
6th	i = 6	false	The loop is terminated

---

Example 3: Find the sum of first n Natural Numbers

// C++ program to find the sum of first n natural numbers
// positive integers such as 1,2,3,...n are known as natural numbers

#include <iostream>

using namespace std;

int main() {
    int num, sum;
    sum = 0;

    cout << "Enter a positive integer: ";
    cin >> num;

    for (int count = 1; count <= num; ++count) {
        sum += count;
    }

    cout << "Sum = " << sum << endl;

    return 0;
}

Output

Enter a positive integer: 10
Sum = 55

In the above example, we have two variables num and sum. The sum variable is assigned with 0 and the num variable is assigned with the value provided by the user.

Note that we have used a for loop.

for(int count = 1; count <= num; ++count)

Here,

• int count = 1: initializes the count variable
• count <= num: runs the loop as long as count is less than or equal to num
• ++count: increase the count variable by 1 in each iteration

When count becomes 11, the condition is false and sum will be equal to 0 + 1 + 2 + ... + 10.

---

Ranged Based for Loop

In C++11, a new range-based for loop was introduced to work with collections such as arrays and vectors. Its syntax is:

for (variable : collection) {
    // body of loop
}

Here, for every value in the collection, the for loop is executed and the value is assigned to the variable.

---

Example 4: Range Based for Loop

#include <iostream>

using namespace std;

int main() {
  
    int num_array[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  
    for (int n : num_array) {
        cout << n << " ";
    }
  
    return 0;
}

Output

1 2 3 4 5 6 7 8 9 10

In the above program, we have declared and initialized an int array named num_array. It has 10 items.

Here, we have used a range-based for loop to access all the items in the array.

---

C++ Infinite for loop

If the condition in a for loop is always true, it runs forever (until memory is full). For example,

// infinite for loop
for(int i = 1; i > 0; i++) {
    // block of code
}

In the above program, the condition is always true which will then run the code for infinite times.

In the next tutorial, we will learn about while and do...while loop.

In the next tutorial, we will learn about while and do...while loop.

< prev

next >