Operand Type Clash - Int Is Incompatible With Date

I'm getting this error when trying to insert data into a table.

"Operand type clash: int is incompatible with date"

This is the SQL I used to create the table:

Code:
CREATE TABLE customers(
customer_id int IDENTITY(1,1) NOT NULL,
member_yn char(1) NOT NULL,
membership_number int NOT NULL,
date_became_member date NOT NULL,

[Code]....

This is the SQL I am using to add data: (Note that there are two dates in each line, scroll to the side.)

Code:
INSERT INTO customers VALUES ('y', 156, 2010-08-29, 'John', 'Smith', '1235 Main Street, Dunmore, PA 18512', 6963287654, 'jsmith@hotmail.com', 1986-06-23);
INSERT INTO customers VALUES ('y', 159, 04/15/2011, 'Mary', 'Jones', '235 Ardmore Blvd, Pittsburgh, PA 15221', 3429831594, 'jones_mary@gmail.com', 01/12/1992);

Each of the lines above to add data uses a different data format because I tried both, while commenting out the other, hoping for the problem to go away with the change in format.

Here is the SQL code to create a primary key for this table:

Code:
ALTER TABLE customers ADD CONSTRAINT pk_customers PRIMARY KEY (customer_id);