C++ for Loop (With Examples) (2024)

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++

C++ for Loop (With Examples) (1)

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

IterationVariablei Action
1sti = 1true1 is printed. i is increased to 2.
2ndi = 2true2 is printed. i is increased to 3.
3rdi = 3true3 is printed. i is increased to 4.
4thi = 4true4 is printed. i is increased to 5.
5thi = 5true5 is printed. i is increased to 6.
6thi = 6falseThe 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

IterationVariablei Action
1sti = 1trueHello World! is printed and i is increased to 2.
2ndi = 2trueHello World! is printed and i is increased to 3.
3rdi = 3trueHello World! is printed and i is increased to 4.
4thi = 4trueHello World! is printed and i is increased to 5.
5thi = 5trueHello World! is printed and i is increased to 6.
6thi = 6falseThe 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 i = 1; i <= num; ++i) { sum += i; } cout << "Sum = " << sum << endl; return 0;}

Output

Enter a positive integer: 10Sum = 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 i = 1; i <= num; ++i)

Here,

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

When i 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 loopfor(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.

Also Read:

C++ for Loop (With Examples) (2024)

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