Can I use interfaces as dynamic variables?

Go doesn't have dynamic variables.

That said, I would like to know what the variable "a" is, in this program bellow, once I can use it as integer and as string. Even conditionals statements work well with it

package main

import (
	"fmt"
)

func main() {
	var a interface{}
	myInt := 1
	myString := "hi"
	
	a = myInt
	if a == 1 {
		fmt.Println("equals to 1")
	}
	
	a = myString
	if a == "hi" {
		fmt.Println(a)
	}
}

You can use a type switch:

package main

func main() {
   var a interface{} = 1

   switch aType := a.(type) {
   case string:
      println("string", aType)
   case int:
      println("int", aType)
   }
}

<https://golang.org/ref/spec#Type_switches>

To determine what the variable type of 'a' you can make use of reflect.TypeOf(),I recreated your code as follows:

package main

import (
	"fmt"
	"reflect"
)

func main() {
	var a interface{}
	myInt := 1
	myString := "hi"

	a = myInt
	if a == 1 {
		fmt.Println("equals to 1")
		fmt.Println(reflect.TypeOf(a))
	}

	a = myString
	if a == "hi" {
		fmt.Println(a)
		fmt.Println(reflect.TypeOf(a))
	}
}

Output:

equals to 1
int
hi
string