Chapter 80 Hello, World!
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Looking at the green characters displayed in the black screen, Lin Hong is no longer as confused as before this time.
He now knows that the top display is the name and version number of the operating system in this computer.
Lin Hong's operating system on APPLE_II is the latest version of the APPLE_DOS operating system V3.3. Before that, there were V3.1 and V3.2, but the previous version was not so powerful and was based on tape storage. THIS VERSION IS ALSO THE MOST FAMOUS AND WIDELY APPLIED VERSION OF APPLE_DOS. Later, the Apple computer was replaced by PRO_DOS, which was specially customized by Microsoft.
APPLE_DOS is Apple's first disk-based system, in which the talented computer engineer Wozniak is naturally involved in the writing of most of the code.
Looking at the beating green "[" symbol on the monitor, Lin Hong stretched out two index fingers, but looked down at the keys on the keyboard. On the keyboard, the corresponding letters were printed. He pressed a few keys slowly and with difficulty, and the word "CATALOG" appeared slowly and with difficulty on the monitor.
Lin Hong doesn't understand why the letters of the keyboard are arranged like this, and the difference between A and B is so far.
After a long time, he learned that this keyboard layout was called the "QWERTY Curtis Keyboard", which was invented in the mid-19th century and was originally designed for mechanical typewriters.
The reason for such a layout is the structure of the mechanical typewriter. The structure of the type lever determines that when two typewriters in close position are pressed at the same time, it will be stuck, but the same problem will not occur when the two typed characters are far apart. Later, after the emergence of the computer, this layout continued.
After struggling to enter this command, Lin Hong pressed the ENTER key, and there was finally a change on the display. A long list was immediately displayed. This is a directory display command, which is exactly what is installed in the disk.
Seeing this result, Lin Hong smiled happily.
This is the first computer operation command he entered. Although the process is very simple, it still makes him feel very excited and excited.
Look at the computer under its own operation, and then begin to react. This sense of conquest that everything is under its own control is difficult to describe in words.
This may be the main reason why boys like all kinds of toys and machines.
Next, Lin Hong began to test all the commands one by one according to what was said in the reference book, and then observed the results. Looking at the information constantly flashing on the monitor, the sense of achievement in his heart is beyond words.
APPLE_DOS operating system is relatively simple, and there are only a few system commands to turn over and over, such as the "CATALOG" used by Lin Hong before, which means "directory" in English, and the function is to display the file directory in the disk. THERE IS ALSO "INTBASIC", WHICH IS TO ENTER THE PROGRAMMING STATE OF INTAGER_BASIC LANGUAGE. AFTER ENTERING THIS COMMAND, YOU CAN START TO WRITE CODE FOR PROGRAMMING.
The so-called system commands are actually small software. The operating system usually comes with some common software, which is bound to the system, which becomes a system command.
If you are not satisfied with these commands in the system, you feel that you can implement the same function in a better way. You can also write such a small tool by yourself, and then replace the original software.
After playing the system commands for a while, Lin Hong began to practice programming in BASIC language.
The language of computer programming, as the name implies, is the language between people and computers. It was invented so that it could be easily understood. When computers were first invented, those fierce people directly operated computers in machine language.
Programming languages can be roughly divided into low-level languages and high-level languages, while low-level languages include machine languages and assembly languages.
The low level here does not mean that the language function is not strong, but to distinguish it from the difficulty that beginners can master. In fact, the functions of low-level languages are more powerful, and the programs written are more efficient.
High-level language is a language that appeared later. The purpose is to make people better understand. It is very close to the words that people usually write.
BASIC is a kind of high-level language. It is the abbreviation of "Beginner's_All-purpose_Symbolic_Instruction_Code", which means "all-round symbolic instruction code for beginners" in Chinese.
This language is a high-level language created by two American computer scientists specifically for college students on campus, in order to make it easy for college students to use computers. Although BASIC had only dozens of statements in the early days, because BASIC was relatively easy to learn at that time, it quickly moved from campus to society and became the preferred language for beginners to learn computer programming.
Later, computer engineers and experts from some computer companies expanded BASIC, allowing BASIC to have more complex functions. Apple's INTEGER_BASIC was developed on this basis by the cooperation of Wozniak and two other colleagues.
For beginners, the BASIC language is obviously the best choice, which is also the most popular programming language in the 1980s.
Lin Hong directly typed two lines of code under the command prompt:
01_PRINT_"HELLO,WORLD!"
02_END
Then, he typed the "RUN" command directly in the third line.
When I saw the next line, "HELLO, WORLD!" immediately appeared. The content.
"Hello, world!" Lin Hong clenched his fist very happily and read it aloud according to the English in the monitor.
Although there has been such interface results in the manual for a long time, it feels different to operate it himself.
This is just an extremely simple applet. No matter what language you learn, when every beginner learns programming, basically the first program is "HELLO, WORLD", which has basically become a custom habit agreed by programmers.
"Hello, world!"
This is such a simple program. Even if there is no foundation, beginners can easily understand it, but it is not pale. It has the distinctive characteristics of a programming language, reflecting the most basic ideas and characteristics of a programming language.
This seems to be a cry of beginners to the computer world, marking their step into this wonderful artificial world from now on, including announcements and the joy of beginners experiencing the first computer program in their lives.
Lin Hong's mood at this moment is like this. He feels that these two simple words just say what he is thinking at this moment.
The origin of "hello, world" can be traced back to 1972. Brian_Kernighan, a famous researcher at Bell Labs, first used this example when writing the "B language (the predecessor of C language) tutorial and guidance", and later he used this example in the C language tutorial. This example was used once, and since then, it has been widely spread.
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