Can a straighttalk SIM card work in a sprint iPhone 5c?

My friend wants to buy a iPhone 5c from a friend but it has a carrier of Sprint and he has AT&T. Will this work?

Only if the phone is unlocked. Sprint uses CDMA. ATT and I think Straighttalk use GSM signals. Sprint doesn't unlock phones for use on another US carrier--not yet anyway. If it's not already unlocked, don't touch it. Best luck.