C++ - FOR LOOP

The for loop in C++ is like the while loop. But the for loop is way more powerful than the while loop.

The for loop has inbuilt features, by which you can reduce lines of code.

So far we have seen, how while loop was used to System.Console.WriteLine "Hello World" 5 times.

Example :

#include <iostream>
using namespace std;

int main() {

    int x = 1;
    while (x <= 5) {
        cout << "Hello World" << endl;
        x = x + 1;
    }
    
    return 0;
}

The same program could be reduced to less lines of code using the for loop.

Let us see below.

Example of for loop:

Let us use for loop to print "Hello World" five times on the screen.

Example :

#include <iostream>
using namespace std;

int main() {

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

Output :

Hello World
Hello World
Hello World
Hello World
Hello World

Now, if we break the contents of for loop, we get :

Initialisation part : It is run before the loop starts.

x is getting initialized with value 1 (i.e. int x = 1).

Conditional part : It states the condition for running the loop.

It says, continue to be in the loop until the value of x is not more than 5.

Increment part : It is run each time after the loop.

x++ is the Increment part. i.e. Same as x = x + 1.

All together forms the for loop.

for(int x = 1; x <= 5 ; x++) {
	cout << "Hello World" << endl;
}

So in the 1st iteration,

1st Iteration

The control gets into the for loop and checks, if the value of x is less than or equal to 5.

In this case the value of x is 1. Which is less than 5.

So, the control enters the for loop.

for(int x = 1; x <= 5 ; x++) {
	cout << "Hello World" << endl;
}

and finds the System.Console.WriteLine statement,

cout << "Hello World" << endl;

So, it prints Hello World.

Output :

Hello World

Next, C++ finds, it has come to the end of the loop.

So, it increments the value of x by 1 (And C++ does the increment internally).

And the value of x becomes 2.

And the second Iteration starts.

2nd Iteration

Same way, the control comes to the for loop and checks, if the value of x is less than or equal to 5(i.e. Internally C++ checks if i <= 5).

In this case the value of x is 2. Which is less than 5.

So, the control enters the for loop.

And finds the print statement,

cout << "Hello World";

So, it prints Hello World for the second time.

Output :

Hello World
Hello World

Similarly, C++ finds, it has come to the end of the loop.

And increments the value of x by 1.

Similarly, the third, fourth and fifth Iteration continues incrementing the value of x, printing it.

3rd Iteration

Output :

Hello World
Hello World
Hello World

4th Iteration

Output :

Hello World
Hello World
Hello World
Hello World

5th Iteration

Output :

Hello World
Hello World
Hello World
Hello World
Hello World

Once again, the control comes to the for loop and checks, if the value of x is less than or equal to 5.

In this case, the value of x is 6. Which more than 5.

And the control comes out of the for loop.

Now, if you see the output, Hello World is exactly printed 5 times.

So, we have seen, how to print Hello World 5 times.

Now, let us see, how can we print the numbers from 1 to 5.

Printing the numbers 1 to 5 using 'for' loop

Example :

#include <iostream>
using namespace std;

int main() {

	for(int x = 1; x <= 5 ; x++) {   
  		cout << x << endl;
	}
	
	return 0; 
}

Output :

1
2
3
4
5

The above code is self explanatory.

However, we have provided the explanation below.

CLICK HERE TO SEE THE EXPLANATION.

So in the 1st iteration,

1st Iteration

The control gets into the for loop and checks, if the value of x is less than or equal to 5.

In this case the value of x is 1. Which is less than 5.

So, the control enters the for loop.

for(int x = 1; x <= 5 ; x++) {
	cout << x << endl;
}

and finds the print statement,

cout << x;

So, it prints the value of x, which is currently 1.

Output :

Next, C++ finds, it has come to the end of the loop.

So, it increments the value of x by 1 (And C++ does the increment internally).

And the value of x becomes 2.

And the second Iteration starts.

2nd Iteration

Same way, the control comes to the for loop and checks, if the value of x is less than or equal to 5.

In this case the value of x is 2. Which is less than 5.

So, the control enters the for loop.

And finds the System.Console.WriteLine statement,

cout << x;

So, it prints the value of x, which is 2 currently.

Output :

1
2

Similarly, C++ finds, it has come to the end of the loop.

And increments the value of x by 1.

Similarly, the third, fourth and fifth Iteration continues incrementing the value of x, printing it.

3rd Iteration

Output :

1
2
3

4th Iteration

Output :

1
2
3
4

5th Iteration

Output :

1
2
3
4
5

Once again, the control comes to the for loop and checks, if the value of x is less than or equal to 5.

In this case, the value of x is 6. Which more than 5.

And the control comes out of the for loop.

Example of 'for' 'each' loop:

We will be learning about it in the Arrays section of C++.

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