Introduction C is a computer language available on the GCOS and UNIX operating systems at Murray Hill and (in preliminary form) on OS/360 at Holmdel. C lets you write your programs clearly and simply _ it has de- cent control flow facilities so your code can be read straight down the page, without labels or GOTO’s; itlets you write code that is compact without being too cryptic; it encourages modularity and good programorganization; and it provides good data-structuring facilities. This memorandum is a tutorial to make learning C as painless as possible. The first part concentrates on the central features of C; the second part discusses those parts of the language which are useful (usuallyfor getting more efficient and smaller code) but which are not necessary for the new user. This is not a ref-erence manual. Details and special cases will be skipped ruthlessly, and no attempt will be made to coverevery language feature. The order of presentation is hopefully pedagogical instead of logical. Users whowould like the full story should consult the C Reference Manual by D. M. Ritchie [1], which should be readfor details anyway. Runtime support is described in [2] and [3]; you will have to read one of these to learnhow to compile and run a C program.