How to create a Terraform with if condition

Virtual Network creation to be deployed based on environment which is declared in locals. Need If condition to deploy below code in different env like Dev/QA & Prod. ... variable "vn_cidr" { description = "CIDR for the VN" default = "10.0.0.0/16" } resource "azurerm_virtual_network" "default"{ name = "virtual-network" address_space = ["${var.vn_cidr}"] } ...