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k3y 10Mar2012 01:24

For Loops [basic]
Hey guys,
I just learned the basics of FOR loops and felt maybe I should share for fellow n00bs out there. A FOR loop can in many cases replace a WHILE loop. This tutorial will show you the relationship between the WHILE loop and the FOR loop, as well as an exercise that I found to be very helpful in learning how to utilize them.
Syntax of a WHILE loop:


i = 1; // initializer
while (i <= 10) // condition
    cout << i << " ";
    i++; // increment

Now in a FOR loop

Syntax of a FOR loop:

for (i=1; i <= 10; i++) //initializer; condition; increment
  cout << i << " ";

Now as you can see the FOR loop is much more condensed then the WHILE loop, and saves some headache. Now it's time for an example code (test a number for primeness):

#include <iostream>
#include <math.h>
using namespace std;
int main()
    int n;
    bool is_prime = true; // boolean (assumes true)

    cout << "Enter a number and press ENTER: ";
    cin >> n;

    for (int i = 2; i <= sqrt(n); i++)
        if (n % i == 0) // if the remainder of n divided by i is zero
        is_prime = false; // then n is not prime

// Print result

    if (is_prime)
        cout << "Number is prime." << endl;
        cout << "Number is not prime." << endl;
    return 0;

Here are a few good exercises to get yourself familiar with WHILE and FOR.
- optimize this program
- find the correct place to put a break statement
- make the same program using a WHILE loop

Hope this can help someone

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