The while...do expression is used to perform iterative execution while a specified test condition is true.
The basic syntax of the while...do loop is as follows.
while test-expression do
body-expression
The test-expression is evaluated; if it is true, the body-expression is executed, and the test expression is re-evaluated. The body-expression must have the type unit. If the test expression is false, the iteration ends.
The following example shows the usage of the while...do expression.
let mutable aa = 10
while (aa < 20) do
printfn "value of aa: %d" aa
aa <- aa + 1
When you execute the above code, you will see the following output.
value of aa: 11
value of aa: 12
value of aa: 13
value of aa: 14
value of aa: 15
F# programming language allows you to use one loop inside another loop which is known as a nested loop.
let mutable a=1;
while(a<=3) do
let mutable b = 1;
while (b <= 3) do
Console.WriteLine("{0} {1}", a, b)
b<- b+1
a<- a+1
When you execute the above code, you will see the following output.
1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3