F # Tutorial-if statement

Last time we used for a for loop processing. This time we learn if statements. A simple example is as follows:

#light
let　add　x　y　=　x　+　y
if　add　2　3　=　5　then　printfn　"2　+　3　=　5"
if　add　2　3　=　6　then　printfn　"2　+　3　=　6"　else　printfn　"2　+　3　!=　6"

When compared with a single =, rather than the usual habit of = =. In addition, it should all be very common. The next example is:

let　even　=　if　10　%　2　=　0　then　true　else　false
printfn　"%A"　even

What you need to notice here is that the IF statement has a value. The action feels similar to the three-mesh operator in C #.

In this case, the value of the IF statement is used as the initial value of the even variable. An if statement with a value cannot be written like this:

Let ten = if add a B < ten then 10

The reason is that the Else branch has no value, is the unit type, so it is inconsistent with the type of the then branch, so there will be a compilation error.

Of course, you can also use else if.

let　lang　=　"VB"
if　lang　=　"C#"　then
　　　　 printfn　"This　is　C#"
else　if　lang　=　"F#"　then
　　　　 printfn　"This　is　F#"
else
　　　　 printfn　"Other"

By the way, the ELIF keyword can be used instead of else if.

if　lang　=　"C#"　then
　　　　 printfn　"This　is　C#"
elif　lang　=　"F#"　then
　　　　 printfn　"This　is　F#"
else
　　　　 printfn　"Other"

You can also use && and | | ：

let　aa　=　1
let　bb　=　2
if　aa　=　1　&&　bb　=　2　then　printfn　"Both　are　true"
if　aa　=　2　||　bb　=　2　then　printfn　"Either　is　true"