How to use For Loop in C++

How to use For Loop in C++

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Updated on Jan 16, 2023 17:37 IST

Loops are used to repeat the same, or similar code number of times. In this article we will discuss how to implement for loops in c++.

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In the world of programming, loops are used to achieve efficient and sophisticated programs. In this article, we will discuss the For loop in C++. This loop repeatedly executes a block of statements in the code. 

We will be covering the following sections today:

So, without further ado, let’s get started!

C++ For Loop

The C++ for loop is a repetition control structure that helps us create a loop that executes a piece of code repeatedly, as specified by the loop.

For Loop Syntax

Following is the syntax for a for loop in C++:

 
for (variable: collection) {
body of the loop
}
Copy code

Here,

  • Initialization – this expression initializes variable(s) and is executed only once.
  • Condition – if the specified test condition is True, the body of the for loop is executed. In case the test condition returns False, the for loop is terminated.
  • Update – this expression updates the value of initialized variables and then the condition is evaluated again.

Let’s look at the following illustration of the for loop flowchart –

2022_07_image-251.jpg

Must Read: What is C++?

Must Check: C++ Online Courses &Certification

C++ For Loop Implementation Examples

Example 1:

 
#include
\n <iostream>\n
\n
using namespace std;\n
\n
int main() {\n
for (int i = 5; i <= 10; i++) {\n
cout << i << " ";\n
}\n
return 0;\n
}\n
\n
\n </iostream>
Copy code

Output 1:

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In the above example, we first initialize a variable i = 5. Then, we specify the condition i <= 10. The loop will run until the test condition holds True.

At last, we specify the update expression i++, which will increment the variable i by 1 during each iteration as long as the condition is True.

Let’s look at the following table to grasp how the loop works:

Iteration Initialization Condition Action and Update
1st i = 5 True 5 is printed. i incremented to 6.
2nd i = 6 True 6 is printed. i incremented to 7.
3rd i = 7 True 7 is printed. i incremented to 8.
4th i = 8 True 8 is printed. i incremented to 9.
5th i = 9 True 9 is printed. i incremented to 10.
6th i = 10 True 10 is printed. i incremented to 11.
7th i = 11 False The loop is terminated.

Example 2:

Find the sum of n-natural numbers using for loop –

 
#include
\n <iostream>\n
\n
using namespace std;\n
\n
int main() {\n
int num, sum;\n
sum = 0;\n
\n
cout << "Enter a positive integer: ";\n
cin >> num;\n
\n
for (int i = 1; i <= num; ++i) {\n
sum += i;\n
}\n
\n
cout << "Sum: " << sum << endl;\n
\n
return 0;\n
}\n
\n
\n </iostream>
Copy code

Output 2:

2022_07_image-253.jpg

In the above code, we have declared two variables num and sum = 0. The variable num takes a value from the user. This value will be the number up to which we want to find the sum of natural numbers.

  • Then, we initialize the variable i = 1.
  • Specify the test condition i <= num so the loop will run from 1 to num.
  • Update expression is also specified as i++ so the value of i increments by 1 in each iteration

When i = 11, the condition returns False, the sum is printed: 1 + 2 + 3 + 4 + 5 + 6 = 21

And, the for loop terminates.

Must Read: Insertion in C++

Range-Based For Loops

From C++ 11 onwards, a new range-based for loop has been introduced that works with collections such as arrays and vectors.

Its syntax is given below:

 
for (variable: collection) {
body of the loop
}
Copy code

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

Let’s understand how this works through an example:

 
#include
\n <iostream>\n
\n
using namespace std;\n
\n
int main() {\n
int num_arr[] = {2, 4, 6, 8, 10, 12, 14, 16};\n
\n
for (int n : num_arr) {\n
cout << n << " ";\n
}\n
\n
return 0;\n
}\n
\n
\n </iostream>
Copy code

Output:

2022_07_image-254.jpg

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

Must Read: Quicksort Algorithm in C++

Infinite For Loop

If the test condition in the for loop is always true, it will keep running infinitely until no memory is left. Look at the following example:

 
// infinite for loop
#include
\n <iostream>\n
\n
using namespace std;\n
\n
int main() {\n
\n
for(int i = 1; i > 0; i++) {\n
cout << i << " ";\n
}\n
\n
return 0;\n
}\n
\n
\n </iostream>
Copy code

Output:

2022_07_image-255.jpg

Must Read: if-else statement in C++

Conclusion

I hope this article was helpful for you in understanding how the for loop is implemented in C++. We also learned about range-based and infinite for loops in C++.

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