In most imperative computer programming languages, a for loop is a control structure which allows code to be executed iteratively. For loops, unlike while loops, are typically used when the number of iterations is known before entering the loop.

Examples

These for loops will calculate the factorial of the number five, 5!, by iterating through all the numbers 1 through 5 and keeping a running product:

QBasic or Visual Basic

 Dim factorial As Long : factorial = 1
 Dim counter As Integer
 For counter = 1 To 5
   factorial = factorial * counter
 Next
 Print factorial

C or C++

 unsigned long factorial = 1;
 for (unsigned int counter = 1; counter <= 5; counter++)
   factorial *= counter;
 printf("%i", factorial);

Python

 factorial = 1
 for counter in range(1, 6):    # range() gives values to one less than the second argument
   factorial *= counter
 print factorial

Java, Csharp

The syntax for the for loop is the same for Java and Csharp

 long factorial = 1;
 for (int counter = 1; counter <= 5; counter++)
   factorial *= counter;

Output of the result in Java

 System.out.println(factorial);

In Csharp

 System.Console.WriteLine(factorial);

JavaScript

var factorial = 1;
for (var counter = 1; counter <= 5; counter++){
  factorial *= counter;
document.write(factorial);
}

Perl

my $factorial = 1;
for ( my $counter = 1; $counter <= 5; $counter++ ) {
    $factorial *= $counter;
}
print $factorial;

Pascal

 program Factorial
 var
   Counter, Factorial: integer;
 begin
   Factorial := 1;
   for Counter := 1 to 5 do begin
     Factorial := Factorial * Counter;
   end;
   Write(Factorial);
 end.

Equivalence with while loops

A for loop can always be converted into an equivalent while loop by incrementing a counter variable directly. The following pseudocode illustrates this technique:

 factorial := 1
 for counter from 1 to 5:
     factorial := factorial * counter

is easily translated into the following while loop:

 factorial := 1
 counter := 1
 while counter <= 5:
    factorial := factorial * counter
    counter := counter + 1

See also

• While loop
• Do while loop
• Loop counterde:For-Schleife

ja:For文