The for Loop

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The for Loop

For loops use an iteration variable. They are ideal when looping over many numbers in order with a definite terminating condition. No collection of elements is required. But we can use the variable to index a separate collection. This iteration variable allows more flexibility than foreach.

Example
This example program loops using the for-loop construct in the C# language. The name of the variable “i” is a convention. Because of this, it is easier for other programmers to understand than unusual variable names in many cases.

The program shows an increment for-loop, a decrement for-loop, a for-loop that adds two the variable, and a for-loop that subtracts two from the variable. The example shows also the exact output of this program when it is executed in the Common Language Runtime.

using System;

class Program
{
static void Main()
{
//
// Shows five ‘for int i’ loops.
//
Console.WriteLine(“— For 1 —“);
for (int i = 0; i < 10; i++)
{
Console.WriteLine(i);
}
Console.WriteLine(“— For 2 —“);
for (int i = 10 – 1; i >= 0; i–)
{
Console.WriteLine(i);
}
Console.WriteLine(“— For 3 —“);
for (int i = 0; i < 10; i += 2)
{
Console.WriteLine(i);
}
Console.WriteLine(“— For 4 —“);
for (int i = 10 – 1; i >= 0; i -= 2)
{
Console.WriteLine(i);
}
Console.WriteLine(“— For 5 —“);
for (int i = 0; i < (20 / 2); i += 2)
{
Console.WriteLine(i);
}
}
}

Output

— For 1 —
0
1
2
3
4
5
6
7
8
9
— For 2 —
9
8
7
6
5
4
3
2
1
0
— For 3 —
0
2
4
6
8
— For 4 —
9
7
5
3
1
— For 5 —
0
2
4
6
8

The for-loop construct is followed by parentheses with three statements separated by semicolons. When the for-loops are encountered, the first of the three statements is executed. The for-loop shown first in the example will first has its “int i = 0” statement executed. The loop will start with its iteration variable set to zero.