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Geekpedia » C++ Tutorials » Introducing the 'for' loop

Introducing the 'for' loop

A really small tutorial introducing the 'for' loop, good for C++ newbies and programming beginners.

On Saturday, March 13th 2004 at 05:59 PM

By Andrew Pociu (View Profile)

(Rated 3.6 with 8 votes)

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In this tutorial I expect you to have a little knowledge about programming, but to understand at least the C++ variables and other basic information.

Like in any other programming language, loops are very useful for repeating tasks. For is probably the best example of a loop.

In this example we will see how to output a string ten times. We make use of ‘cout’ only once.




// Demonstrating the for loop



#include <iostream>

using namespace std;



int main()

{

    int counter;    // This variable will be changed by the loop



    for (counter = 0; counter < 10; counter++)    // Initialize to 0, check the current value and increment it

    {

        cout << "Loop number " << counter << "\n";    // Output some text and the value the variable holds

    }

    return 0;

}

Let’s dissect the code a little:

int counter - create a variable that will hold a different value each loop.
for (counter = 0 - initialize the variable to the value 0.
counter < 10 - check if the variable holds a value smaller than 10. If it does, the loop continues.
counter++ - increment the variable by one. As you may know, it’s equal to counter = counter + 1, but shorter.

The variable continues to be incremented, until it reaches 10. When the variable holds 10, the ‘counter < 10’ expression returns false, and the loop stops.

Check the following example:




// More about the for loop



#include <iostream>

using namespace std;



int main()

{

    cout << "Please input the starting number: ";

    int start_num;

    cin >> start_num;

    cout << "Please input the ending number: ";

    int end_num;

    cin >> end_num;

    int counter;

    for (counter = start_num; counter <= end_num; counter++)

    {

        cout << counter << "\n";

    }

    return 0;

}

for (counter = start_num - initialize the variable to the value of start_num.
counter <= end_num - check if the variable holds a value smaller or equal than the end_num variable. If it does, the loop continues.
counter++ - increment the variable by one.

This time the loop checks if the variable is smaller or equal, not just smaller.
If start_num was 3 and end_num was 9, and we used a counter < end_num condition, the result would be this:

Because when counter hits the value 9, the condition returns false. 9 is not smaller than 9, it is equal.

This is the result because when the counter hits the value 9, the condition returns false. 9 is not smaller than 9, it is equal.

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Current Comments

by Ehi on Thursday, June 17th 2004 at 07:03 PM

Hello, I like your article. However I modified it and I would like to see you to see what is wrong with this code#include <iostream>
#include <stdlib.h>
using namespace std;
using std::cout;
using std::cin;
using std::endl;
int main()
{
char myname;
int numb;

cout<<"Please type your name:";
cin>>myname;
cout<<endl;
cout<<"How many times do you want your name to be displayed: ";
cin>>numb;
cout<<endl;
cout<<"You want "<<myname<<" to be displayed "<<numb<<" times.";
system("pause");
}
Thank you.

by Ehi on Thursday, June 17th 2004 at 07:05 PM

Better still can I send it to you by email, because some of the syntax did not appear.

by ruud breukink on Friday, November 5th 2004 at 05:32 PM

Can I make variable designations in a for loop ?

meaning :

for (int i=0; i<Num; i++) {
string name = "test"+ (string)i;
ClassSomething* name = nem ClassSometing();
}

cheers, ruud

by aidi on Thursday, December 23rd 2004 at 12:01 AM

it very good for elementry class. i will copy your tutorial to development knowledge me. thank for you. i hope you can send information about programming C++ me at next time.

aidi

politeknik state of lhokseumawe
indonesia

by babyblue on Tuesday, September 9th 2008 at 06:31 AM

can u make an old version of c ... the truth is i cant understand the c language coz im only a 1st year college.. ^^

my professor teach only the old c like...

#include <iostream.h>
#include <stdio.h>
#include <conio.h>

main()
{
clrscr();

int x;
cout <<"input numbers 1-10";

for (x=0 ; x<=10 ; x )
cout<<x<<" ";
getch();
}

.. "like this??" ^^,

hmmm... thx...