Question: What is the difference between a compiler and a linker in C?

Answer: 
The compiler converts code written in a human-readable programming language into a machine code representation which is understood by your processor. This step creates *object* files.

Once this step is done by the compiler, another step is needed to create a working executable that can be invoked and run, that is, associate the function calls (for example) that your compiled code needs to invoke in order to work. For example, your code could call `sprintf`, which is a routine in the C standard library. Your code has nothing that does the actual service provided by `sprintf`, it just reports that it must be called, but the actual code resides somewhere in the common C library. To perform this (and many others) linkages, the *linker* must be invoked. After linking, you obtain the actual executable that can run.
A compiler generates object code files (machine language) from source code.

A [linker](http://en.wikipedia.org/wiki/Linker_%28computing%29) combines these object code files into an executable.

Many IDEs invoke them in succession, so you never actually see the linker at work. Some languages/compilers do not have a distinct linker and linking is done by the compiler as part of its work.