Delphi Study Notes (1)

I tried to learn Delphi in college, but I was born with a head-and-tail character. Now, I hope I can make some achievements in my work.
Delphi programming uses the Object Pascal language. All the tutorials I have read are simple and easy to understand, but I seem confused. After all, it is now the world of C series.

Object Pascal has multiple predefined data types. You can describe any of these types of variables:
Integer: the integer value ranges from-32768 to 32767, which occupies 2 bytes of memory. The integer value ranges from-128 to 127, which occupies 1 byte memory. The longint value ranges from-2147443648 to 2147483647, which occupies 4 bytes of memory; byte ranges from 0 to 255, accounting for 1 byte; Word ranges from 0 to 65535, accounting for 2 bytes of memory. They are all numbers without decimal digits.
Real Type: single can contain 7 to 8 Valid decimal places, occupying 4 bytes of memory; double class can include 15 to 16 valid decimal places, occupying 8 bytes of memory; the extended type contains 19 to 20 valid decimal places, which occupies 10 bytes of memory. The comp can contain 19 to 20 valid decimal places, occupying 8 bytes of memory. The preceding real number type can be used only when option [n +] 8087/80287 is enabled. Real can contain 11 to 12 decimal digits, occupying 6 bytes of memory. It is used only when it is compatible with Borland Pascal. Otherwise, double or extended should be used.
Boolean: Boolean, which contains only true or false values and occupies 1 byte of memory.
Character Type: Char, an ASCII character; string type: A string can contain up to 255 ASCII characters.
Pointer: pointer, which can point to any specific type.
String: pchar, a pointer to a string ending with zero.
In addition to predefined types, Delphi also has custom types.