CS50 ide do not compile sometime

cs50

#1

Hello,i am solving the “caesar cipher” problem of pset2 of cs50 but when I want to compile, it prompt this particular message "make: *** No rule to make target `caesar’. Stop. " even though I am in proper directory and also saved the file.Helping hand required !! I often run into this problem.Can anyone point out what’s the problem here?