How can I reference a variable in `main.tf`? - terraform

Question

I have two terraform files main.tf and var.tfvars:
main.tf:
provider "google" {
project = var.project_id
region = var.gcp_region
}
provider "aws" {
region = var.aws_region
alias = "aws"
}
vars.tfvars:
variable "gcp_region" {
type = string
default = "asia-southeast1"
}
variable "aws_region" {
type = string
default = "ap-southeast-2"
}
variable "project_id" {
type = string
default = "test-oidc-arosha"
}
when I run terraform apply, I got below error:
Error: Reference to undeclared input variable
│
│ on local.tf line 6, in locals:
│ 6: state_backet = "${local.component_name}-${local.part_name}-deployment-${var.aws_region}-${data.aws_caller_identity.current.account_id}"
│
│ An input variable with the name "aws_region" has not been declared. This variable can be declared
│ with a variable "aws_region" {} block.
╵
╷
│ Error: Reference to undeclared input variable
│
│ on main.tf line 2, in provider "google":
│ 2: project = var.project_id
│
│ An input variable with the name "project_id" has not been declared. This variable can be declared
│ with a variable "project_id" {} block.
╵
╷
│ Error: Reference to undeclared input variable
│
│ on main.tf line 3, in provider "google":
│ 3: region = var.gcp_region
│
│ An input variable with the name "gcp_region" has not been declared. This variable can be declared
│ with a variable "gcp_region" {} block.
I don't understand why I got this error even I already specified the default values for each variable.
My terraform version is:
$ terraform --version
Terraform v1.0.0
on darwin_amd64
+ provider registry.terraform.io/hashicorp/aws v3.45.0
+ provider registry.terraform.io/hashicorp/google v3.72.0

Answer 1

Change the name of you vars.tfvars file to variables.tf and it should pick up the default value. .tfvars files are for inputs to variables which are in turn defined in the variables.tf file (or any .tf file actually, doesn't matter what you call it.)

Answer 2

you need to add variable definition to your main.tf and then use your variable in var.tf approapriately
example
variable "aws_region" {
type = string
default = "ap-southeast-2"
}
var.tfvars
example
aws_region = {
Name = "created by jatin/terraform",
instance_type="t2.micro"
}