Dear Murugan
Cracks in building are a common occurrence and it is important to understand the causes and the measures to be taken for their prevention.Materials such as bricks,mortar and concrete, which contain considerable quantity of water at the time of construction, dry out subsequently and under go major contraction. If we take precaution during costruction these may be minimise see link below
http://www.gharexpert.com/home/HOW_TO_PREVENT_CRACKS_IN_BUILDING.aspx
http://www.gharexpert.com/articles/Cracks-718/Which-Various-Reasons-Cracks-in-Buildings-_0.aspx
http://www.gharexpert.com/articles/Cracks-1468/How-To-Repair-Cracks_0.aspx