How to typecast a struct field in Go lang : My struct:

type User struct {

FirstName string `json:"firstname, omitempty" validate:"required"`

LastName string `json:"lastname, omitempty" validate:"required"`

NumberofDays  int   `json:"numberofdays, string" validate:"min=0,max=100"`

}


Value for NumberofDays is passed as string from the server but I want to check if it is within range and store as int. 

Ex: user := &User{"Michael","Msk","3"}
 
I'm getting 'cannot unmarshal string into Go value of type int'. 

I'm not sure how to typecast to int and do the validation