Add information about conditional statements

Author: mfbmina

README.md

@@ -36,7 +36,7 @@ I believe to get a good understanding, you can follow this order:
 - [Constants & variables](https://github.com/mfbmina/data-structures-algorithms-go/blob/main/constants_and_variables.go)
 - [Stdin & stdout](https://github.com/mfbmina/data-structures-algorithms-go/blob/main/stdin_stdout.go)
 - [Arrays](https://github.com/mfbmina/data-structures-algorithms-go/blob/main/array.go)
-- [Conditional structures]()
+- [Conditional statements](https://github.com/mfbmina/data-structures-algorithms-go/blob/main/conditional_statements.go)
 - [Loops]()
 - [Pointers](https://github.com/mfbmina/data-structures-algorithms-go/blob/main/pointers.go)
 - [Structs](https://github.com/mfbmina/data-structures-algorithms-go/blob/main/structs.go)

conditional_statements.go

@@ -0,0 +1,62 @@
+package main
+
+import "fmt"
+
+// Conditionals help us to choose an action based on the data that we have.
+//
+// To have conditional statements, we need to have our conditional operators.
+// Conditional operators tell you which comparisons you are allowed to do.
+// In Golang, we have the following operators:
+// - `A == B`: returns `true` if A is equal to B
+// - `A != B`: returns `true` if A is different from B
+// - `A >  B`: returns `true` if A is higher than B
+// - `A >= B`: returns `true` if A is higher or equal to B
+// - `A <  B`: returns `true` if A is lower than B
+// - `A <= B`: returns `true` if A is lower or equal to B
+//
+// We also have logical operators:
+// - `X && Y`: `&&` is the logical operator `AND`. It expects both expressions to be true.
+// - `X || Y`: `||` is the logical operator `OR`. It expects one expression to be true.
+// - `!X`: `!` is the operator `NOT`. It negates the value of the expression. If the expression is already false, it becomes true. `!false == true`.
+//
+// In Golang we have two ways of doing conditional statements: `if/else` and `switch/case`.
+func main() {
+  var age int
+  var country string
+  fmt.Println("How old are you?")
+  fmt.Scanln(&age)
+  fmt.Println("Where are you from?")
+  fmt.Scanln(&country)
+
+  // One good example is asking your age before visiting some websites.
+  // If the person is a minor, we shouldn't allow him/her to visit the page.
+  // This case is what we call `if/else` statement because it should choose between actions by evaluating expressions as true or false.
+  // It will always execute the first true condition and if no condition is satisfied, it will execute the else.
+  if age >= 21 {
+    // If the provided age is equal or higher to 21, it will print "Welcome!"
+    fmt.Println("Welcome!")
+  } else if age >= 18 && country != "US" {
+    // If the provided age is equal or higher to 18 and the user is not from the US it will print the message.
+    fmt.Println("Quite young but still welcome!")
+  } else {
+    // If the age is below 18 it will print the following message.
+    fmt.Println("hmmm... maybe you should not be allowed on here!")
+  }
+
+  var animal string
+  fmt.Println("What is your favorite animal?")
+  fmt.Scanln(&animal)
+
+  // Sometimes, we do not want to check if something is true or false, but to check if it has a specific value.
+  // This is the best option to use the switch statement.
+  switch animal {
+  case "dog":
+    fmt.Println("Dogs bark, right?")
+  case "cat":
+    fmt.Println("Meow!")
+  case "fish":
+    fmt.Println("I've no clue how a fish sounds...")
+  default:
+    fmt.Println("Hm... I need to upgrady my animal list...")
+  }
+}