[author : Ron Cain] #C #Programming #Listing #Fortran

Extract : «  I had to have a compiler for my home computer.

There was no doubt about it: after programming nearly every day in BLISS and then reading about C, PASCAL, LISP, and all the other various languages becoming available, it made no sense at all to continue programming in assembly language.

However, the question arose: Which language?

Surprisingly, the decision was not difficult. Since I do mostly system type programming (editors, music-board drivers, modem talkers, faster versions of LIFE, etc.) rather than application programming (accounting programs, solar eclipse predictors, etc.), the choice boiled down to two: C or BLISS. Besides having the most esoteric names of the group, both possess the strengths of system programming languages. Which is to say they both have a slightly better notion of computer architectures than strictly application oriented languages in terms of accessing bytes and words, and neither wastes time doing “garbage collection” or keeping track of legal array subscripting. Both are intended to produce fairly fast (usually inline) code to get the job done with the least amount of overhead.

After looking around the marketplace, I decided C was the appropriate choice if I expected to produce code usable by others. However, another thing also became obvious: the C compilers available either cost a lot of money, ran only on CP/M, or both. Having neither a lot of money nor CP/M (the second by choice), I had to think of an alternate approach.

The first step came by way of the Tiny-C Interpreter offered by Tiny-C Associates. For a mere $40, I was able to buy the source code of a working C interpreter. I intended to use it to run the C programs I would write until something bigger and better came along. I sent off the money, got the huge white notebook in the mail, and after a couple weeks of typing, had it up and running. Let me be another of many praising the product. The documentation, clarity of print, and ease of implementation of the thing were all exceedingly good. [...]  »

[author : D. M. Ritchie, S. C. Johnson, M. E. Lesk, B. W. Kernighan ] #C #Programming #Book

Extract : «  C is a general-purpose programming language that has proven useful for a wide variety of applications. It is the primary language of the UNIX* system, and is also available in several other environments. This paper provides an overview of the syntax and semantics of C and a discussion of its strengths and weaknesses.

C is a general-purpose programming language featuring economy of expression, modem control flow and data structure capabilities, and a rich set of operators and data types.

C is not a “very high-level” language nor a big one and is not specialized to any particular area of application. Its generality and an absence of restrictions make it more convenient and effective for many tasks than supposedly more powerful languages. C has been used for a wide variety of programs, including the UNIX operating system, the C compiler itself, and essentially all UNIX applications software. The language is sufficiently expressive and efficient to have completely displaced assembly language programming on UNIX.

C was originally written for the PDP-11 under UNIX, but the language is not tied to any particular hardware or operating system. C compilers run on a wide variety of machines, including the Honeywell 6000, the IBM System/370, and the Interdata 8/32. [...]

*UNIX is a trademark of Bell Laboratories. © 1978, American Telephone and Telegraph Company; Reprinted by permission.  »

[author : Tom Gibson and Scott Guthery] #C #Programming #Method #Book

Extract : «  Perhaps you have heard structured programming described as “go-to-less” programming. Or programming with just if-then-else and do-while control statements. Such remarks oversimplify what structured programming is all about. The essence of structured programming is PROGRAM CLARITY. You can write programs in small, modular parts with easy-to-follow program flow. You can use well-chosen, descriptive variable names. This leads to clear, humanly understandable programs. That is the real objective of structured programming.

We discuss here three principle ideas that make program clarity possible. These are: modularity, predictable program flow, and local variables.

MODULARITY in software is just as important as modularity in hardware. It makes it humanly possible to deal with complexity. A module is a brick or atom used for building bigger modules. Seen from within, a module may be very complex but from the outside it is an indivisible whole. Software modularity is achieved through the use of FUNCTIONS.

PROGRAM FLOW is predictable if you can point to any statement and easily answer the question “under what conditions is this statement executed?” This is particularly important if the program is 20 or 30 pages long and still has bugs. Scanning the whole program and drawing arrows is no fair. That’s not considered an easy way to answer the question. Predictable program flow can be achieved in many ways. In C, it is done with COMPOUND STATEMENTS.

Functions also make it possible to hide variables used in a strictly local context. The variable n is very popular; it’s used frequently to count things. Have you ever had a program blow up because you were using n in two places for two purposes? The fix was to change one of them to nl. A better idea is in the concept of LOCAL and GLOBAL variables.

David Gries suggests structured programming be called “simplicity theory,” and characterizes it as “an approach to understanding the complete programming process” [Gries 1974]. As a pleasant dividend, structured programming is more enjoyable than monolithic programming. It should certainly, therefore, be a part of personal computing. To begin our look at tiny-c as a structured programming language, let’s look at the foundation of functions and predictable program flow — the compound statement. [...]  »

[author : Lee Barker] #Listing #Assembly

Extract : «  OSI’s Fortran, Basic, and Cobol CP/M package was purchased a year ago and a number of problems encountered. The most serious of these being that Cobol wouldn’t work. Last month the updated version was obtained with some of the old problems fixed, and a few new ones added. Enclosed is a modified hsting of the OSI’s 10 routines that corrects a few of these problems. [...]  »

[author : Dennis Allison ] #Listing #C

Extract : «  Algorithms are published in many places. For many years there was an algorithms column in the Communications of the ACM (it’s now published as part: of ACM’s Transactions on Mathematical Software). I learned a lot reading those algorithms and trying to understand how they work); they are still worth reading and understanding.[...]  »

[author : Andrew Bender] #Listing #Assembly

Extract : «  Often there is a need to prepare floppy disks, or removable packs, with sets of “standard” predetermined files. One example is the construction of “library disks;” another is the preparation of distribution copies of programs. Being in the position of needing both library disks and distribution disks I had used the “COP” routine supplied with MITS DOS. This routine is: quite fast and very flexible; however, it is difficult to use. It must be invoked each time you want to copy a single file:; six parameters must be given for each file copied. If anything goes wrong during the copy or assignment of files, the routine unforgivingly aborts with little or no information as to why it failed. [...]  »

[author : Robert W. Dea] #Listing #BASIC

Extract : «  This program will accept 8080 mnemonics as input and translate them to the corresponding Z80 mnemonics; it was written in Digital Group Business Basic. I currently own a Digital Group Z80 computer system with the 50K bytes of memory, 4 digital PHI decks, and a 30 cps printer.

The 8080 to Z80 translator consists of a language skeleton and a grammar analyzer. The language skeleton in this case defines the structure of Intel 8080 mnemonics and the modified Digital Group Z80 mnemonics. The grammar analyzer parses the language skeleton in a top down left right process and verifies the correctness of the input mnemonic and generates the corresponding Z80 output. The translator is totally driven by the language skeleton and can be easily changed to translate a subset of the Z80 mnemonics to 8080 mnemonics. In fact it can be modified to perform any translation which consists of a one-to-one transformation. [...]  »