Take a look in the standard library header, stdlib.h:
stdlib.h
atoi()
atof()
Wiki probably not the best reference for the C standard library, but I haven't had my coffee yet this morning and you get the idea.
However, atoi() is not clearly defined or part of the actual "Standard," but is usually included in the standard library of C.
Check MikroC's library documenation for details.
Also, there are also plenty of short routines available, in the embedded C world, if you're trying to conserve precious program memory and other limited resources to accomplish the task with limited resources.
If in the future you happen to by making the conversion the other direction. Be advised, I would avoid the use of their FloatToStr() and IntToStr() functions, the both require large arrays of char and seem to create more problems than they solve.
A form of sprintf(), which is defined by the "Standard" and usually included in the stdio.h, can achieve a more effective result. Sprintf() can be a memory hog and is usually accompanied by several limited and smaller footprint versions in embedded C compilers.
sprintf()