C and Objective-C When you run a program, a file is copied from the file system into memory (RAM), and the instructions in that file are executed by your computer. Those instructions are inscrutable to humans. So, humans write computer programs in a programming language. The very lowest-level programming language is called ! . In assembly code, you describe every step that the CPU (the computer’s brain) must take. This code is then transformed into (the computer’s native tongue) by an . Assembly language is tediously long-winded and CPU-dependent (because the brain of your new iMac can be quite different from the brain of your well-loved, well-worn PowerBook). In other words, if you want to run the program on a different type of computer, you will need to rewrite the assembly code. To make code that could be easily moved from one type of computer to another, we developed “high- level languages.” With high-level languages, instead of having to think about a particular CPU, you can express the instructions in a general way, and a program (called a " ) will transform that code into highly-optimized, CPU-specific machine code. One of these high-level languages is C. C programmers write code in the C language, and a C compiler converts the C code into machine code.