One of my friend connected me to the wifi in our area . Now my computer automatically connects to that wifi. I don't need to enter the password. I wanted to browse internet using my android phone. Since i don't know the password i can't connect to the wifi network. Is there any file/folder where the password for the wifi is saved on windows-7 pc ?
In the computer that can connect to the network, type Manage wireless networks into the start menu search. Right click on the properties for the network you want and click Properties. In the security tab you should see an option to Show characters.
This will reveal your WiFi password that computer remembers.
This is the same process as described in the answer for Change the password Windows 7 has stored for a wireless network. Thanks @iglvzx for pointing this out.
You can retrieve a hex encoded version (which works if you input it into the usual places) with wireless key view. The documentation for this states that the keys are stored either in the registry or the filesystem as follows
The location for 7 and vista should be the same.