Speech / Voice Recognition

i wanted to program a basic speech/voice recognition in C. I have no idea where to start and would love it if you could help me out. It should basicly just answer questions. For example if i ask the program what the weather is like, it should recognize the speech and then tell me the weather. Somequestions i had in mind are:

-What software can i use to start this off ?

-Do i record a bunch of sounds of me saying 'hello' for example, or just record one and the program automaticly detects it ?

-Are there any open source programs like this i should know of ? That way i can edit the sounds files to insert my own recognition files & answer files.

I would also love it if you can recommend any sites or books about this topic.

Thanks in advance !