# Calculate the factorial of a number

These while loops will calculate the factorial of a number: 

## Contents

### Visual Basic / QBasic

```Dim counter as Integer : counter = 5
Dim factorial as Long : factorial = 1
While (counter > 0)
factorial = factorial * counter     'Multiply
counter = counter - 1               'Decrement
Wend
Print factorial                       'Prints out the result.
```

### REALbasic

```Dim counter as Integer = 5
Dim factorial as Integer = 1
While counter > 0
factorial = factorial * counter     //Multiply
counter = counter - 1               //Decrement
Wend
MsgBox Str( factorial )               // Prints out the result.
```

### C or C++

```unsigned int counter = 5;
unsigned long factorial = 1;
while (counter > 0)
{
factorial *= counter--; /*Multiply, then decrement.*/
}
printf("%i", factorial);
```

### Perl

```my \$counter   = 5;
my \$factorial = 1;
while ( \$counter > 0 )
{
\$factorial *= \$counter--; # Multiply, then decrement
}
print \$factorial;
```

Very similar to C and C++, but the while loop could also have been written on one line:

```\$factorial *= \$counter-- while ( \$counter > 0 );
```

### Tcl (Tool command language)

```set counter 5
set factorial 1
while {\$counter > 0} {
set factorial [expr \$factorial * \$counter]
incr counter -1
}
puts \$factorial
```

### Java, Csharp

The code for the loop is the same for Java and Csharp:

```int counter = 5;
long factorial = 1;
while (counter > 0)
factorial *= counter--; // Multiply, then decrement.
```

For Java the result is printed as follows:

```System.out.println(factorial);
```

The equivalent in C# is:

```System.Console.WriteLine(factorial);
```

### OCaml

```# let rec f n = if n=0 then 1 else n*f(n-1);;
val f : int -> int = <fun>
```

For example:

```# f 5;;
- : int = 120
```

### Pascal

```program Factorial
var
Counter, Factorial: integer;
begin
Counter := 5;
Factorial := 1;
while Counter > 0 do begin
Factorial := Factorial * Counter;
Counter := Counter - 1;
end;
Write(Factorial);
end.
```

### Python

```counter = 5
factorial = 1
while counter>0:
factorial *= counter
counter -= 1
print factorial
```