## 5. if and for Statements

### Printing out Multiples of a Number

We have mischievously decided to leave out a complete description of `for` loops in this chapter as well. However, it will be provided later. For the time being, ignore the unexplained details and concentrate on the intended purpose of `for` loops: repeating (i.e. iterating). Iteration is what `for` loops do best.

If you happen to be SO impatient, you can take a quick glance here.

Another example of utilizing `for` loops is presented here: a program that prints out the first five multiples of the number 3:

```#include <iostream>
using namespace std;

int main()
{
for(double i=1; i<=5; i++)
cout << i*3 << endl;
}
```

Please type in and execute this program. Upon execution, the following numbers will appear on your screen:

```3
6
9
12
15
```

In the given for loop, the variable `i` gets assigned the values 1, 2, 3, 4, 5 in this exact order. However, in the `cout` statement the value of variable `i` gets multiplied by number 3, and that ultimately results in the desired list of the first five multiples of the number 3.

The variable counting the iterations of a `for` loop (in this example: `i`) is called the loop variable. There is no mandate requiring that it should be named '`i`'. You can use any other valid name. However, it is a common practice to name loop variables with the letters `i`, `j`, `k`.

In the following example we have renamed `i` into `num`, and also slightly redesigned the printout:

```#include <iostream>
using namespace std;

int main()
{
for(double num=1; num<=5; num++)
cout << num << "*3=" << num*3 << endl;
}
```

By executing this program, you should get the following printout:

```1*3=3
2*3=6
3*3=9
4*3=12
5*3=15
```

The real change in this program is in the statement:

```        cout << num << "*3=" << num*3 << endl;
```

The best way to understand the behavior of this program is to imagine that the execution of the `for` loop is suspended in time, for example at the fourth iteration when the loop variable `num` assumes the value 4. To execute the highlighted statement, first we print out the value of the variable `num`, that is the number 4; then we print out the string `"*3="` and finally, the value of the expression `num*3`, which is the number 12. Altogether, the fourth iteration outputs the following on standard output:

```4*3=12
```