The Server name cant be localhost. The Server name is the instance of SQL not the name of the Computer. a lot of people confuses this. There is a Difference between Data Source and servername. The Data Source is the SQL instance and the Servername is the name of the computer. in the Data Source should be the servername display when you try to connect to the sql server using SQl management studio. Copy that and put it here and it will work.
#define A 3// name a constant
long int booking_ID ; ...