``` 80 PRINT total ``` The variable named **count**, is called the *control variable* of a **FOR … NEXT** loop. The effect of this program is that **count** runs through the values **1** (the *initial value*), **2**, **3**, **4** and **5** (the *limit*), and for each one, lines 30, 40 and 50 are executed. Then, when **count** has finished its five values, line 80 is executed. ### STEP The control variable, does not have to increase by 1 each time; you can change this 1 to anything you like by adding a **STEP** clause in the **FOR** command. The most general form for a **FOR** command is: **FOR** *control variable* = *initial value* **TO** *limit* **STEP** *step* where the *initial value*, *limit* and *step* are all *numeric expressions*; things in other words that the computer can calculate as numbers – like the actual numbers themselves, or sums, or the names of numeric variables. So, if you replace line 20 in the program by: ``` 20 FOR count=1 TO 5 STEP 3/2 ``` then **count** will run through the values **1**, **2.5** and **4**. Notice that you don't have to restrict yourself to whole numbers, and also that the control value does not have to hit the limit exactly – it carries on looping as long as it is less than or equal to the limit. Try this program, to print out the numbers from **1** to **10** in reverse order. ``` 10 FOR n=10 TO 1 STEP -1 20 PRINT n 30 NEXT n ``` We have said before that the program carries on looping as long as the control variable is less than or equal to the limit. If you work out what this would mean in this case, you will see that it gives nonsense. The normal rule has to be modified; when the step is negative, the program carries on looping as long as the control variable is greater than or equal to the limit. You must be careful if you are running two **FOR...NEXT** loops together, one inside the other. Try this program, which prints out the numbers for a complete set of six spot dominoes.  ``` 10 FOR m=0 TO 6 20 FOR n=0 TO m 30 PRINT m;":";n;" "; 40 NEXT n 50 PRINT 60 NEXT m ``` You can see that the n-loop is entirely inside the m-loop – they are properly *nested*. What must be avoided is having two **FOR … NEXT** loops that overlap without either being entirely inside the other, like this:  ``` 5 REM this program is wrong 10 FOR m=0 TO 6 20 FOR n=0 TO m 30 PRINT m;":";n;" "; 40 NEXT m 50 PRINT 60 NEXT n ```