How to create multiple subnets automatically with with same subnetmast

I am new to Terraform. I am trying to create a code in which I can create the subnet in loop but cidrsubnet function is not working out as I don’t want to change the subnet mask. For Example: I want to create the subnet with these IPs: Subnet 1:, subnet 2: subnet3: and so on till subnet 8: So is there anyway I can put the the First subnet then it can create rest 8 subnet automatically without me mentioning all subnet CIDR. I am asking as in the other requirement I have work on is to create 16 subnet and I don’t want to put the subnet manually. My Code looks like this:

variable "vpc_id" {
  default = "vpc-123"

#Here add all your 8 CIDR's to the list in "subnet_cidr" and for each one add one entry in "subnet_azs". You can repeat values in "subnet_azs" but not in subnet_cidr"

variable "subnet_cidr" {
  default = ["", "", "", ""]

variable "subnet_azs" {
  default = ["us-east-1a", "us-east-1b", "us-east-1c", "us-east-1c"]

resource "aws_subnet" "my_subnets" {
  count             = 8
  vpc_id            = "${var.vpc_id}"
  cidr_block        = "${element(var.subnet_cidr, count.index)}"
  availability_zone = "${element(var.subnet_azs, count.index)}"