C Expert Programming Chapter 1 C: Through the Fog of Time and Space 1.2 Early Experience of C Language

1.2 Early experience of C language
Array subscripts start from 0 instead of 1.The valid range of a[100] is a[0]~a[99].
 
    C语言的基本数据类型直接与底层硬件相对应。

The auto keyword is obviously a decoration.(only interesting to compiler designers who create symbol table entries) means: "automatically allocate memory when entering a program block" (as opposed to global static allocation or dynamic allocation on the heap) it is the default variable memory allocation mode.

Array names in expressions can be treated as pointers.

float is automatically expanded to double.Although this is no longer the case in ANSI.It has to do with the hardware representation of floating point numbers in PDP-11.First, in a PDP-11 or VAX, converting from float to double is very cheap, just add a word with each 0 bit after it.If you want to convert back, just remove the second word.Second, be aware that in some PDP-11 hardware representations of floating-point numbers there is an operation mode bit (mode bit), you can either only do float operations or only double operations, but if you want to do bothTo switch between the modes, you must modify this bit to change the operation mode.

Nested functions (functions that contain the definition of another function inside of them) are not allowed.

The register keyword.This keyword can give the compiler designer a clue that those variables in the program are hot and can be stored in registers.This design can be said to be a mistake.It is obviously better to let the compiler handle the allocation of registers automatically when each variable is used, than to keep such variables in registers for the lifetime of the declaration.
Complex Language Elements:
Generics and Tasks in Ada
String Handling in PL/I
Templates and Multiple Inheritance in C++

C has evolved from a usage tool to a heavily experimented and tested language.The first C compiler appeared around 1970.As time flies, the UNIX system as its foundation has been widely used, and the C language has also thrived.Its emphasis on low-level operations supported by hardware brought great efficiency and portability, which in turn helped UNIX achieve great success.