C basics: what the language is and where it is used

What C is

C is a small, compiled, general-purpose programming language. Dennis Ritchie created it at Bell Labs in the early 1970s to write the Unix operating system, and it is still the language of operating system kernels, device drivers and language runtimes.

The language itself has few keywords. Everything else comes from a standard library and from the headers of the system you build on, so a C program is a set of functions, types and pointers compiled into one executable file by a compiler such as gcc.

C has no garbage collector: you allocate memory with malloc and release it with free. That is what makes it fast and what makes it demanding.

Where C is used

Operating systems (Linux, Windows, macOS), embedded firmware, databases, compilers and interpreters, network servers and libraries with bindings for other languages are all written in C or expose a C interface.

On this site the language has its own course, a textbook and articles on pointers, structures and sockets.

Hello, world

Save this as hello.c. The main function is where execution begins, and printf writes a line to standard output.

#include <stdio.h> int main(void) { printf("Hello, World!\n"); return 0; }

Compile it and run the executable:

gcc -std=c17 -Wall -Wextra -Wpedantic hello.c -o hello
./hello

Hello, World!

The compiler reports warnings and errors before the program runs; read the first diagnostic and its line number. When the program is ready, continue with the C course, lesson by lesson.

Before you start

Before you start programming, it will be useful to find and read a book about the operating system. The system in which you want to do it.

For example, it is useful to know about the system variable. PATH .

If you want to program in C from Windows You might need an article.

Installation of the GCC compiler in Windows

a.out

If, after compilation, by gcc You have a file. a.out And you don’t know what to do with it:

./a.out

If you want the executable file not to be named after compilation a.out In other words, you will use the option o.

gcc -o new_name code.c

After compilation, you will receive an executable file. new_name It will have to be launched with the help of

./new_name

Number conversion

For beginners, it may seem very surprising to convert numbers. Suppose you enter 9. And you want it printed for you. And you get 57.

To understand this issue, you need to open the ASCII symbol table. reference And find the 9 in it. It corresponds to the hexadecimal number 39. To give you the result, the computer converts 39 to decimal form according to the formula x = 3*16 + 9*1 = 57.

Solving problems from the Kernighan and Ritchie textbook

Bitwise operations

Article author: Arthur Isaev