Built-in ABAP Type List or Predefined ABAP Types for SAP Systems

Predefined ABAP types can be listed as fixed length elementary ABAP type and variable length ABAP data type.
Fixed length build-in ABAP types cover numeric types, character types and hexadecimal types.
In the ABAP Keyword Docementation tool the built-in ABAP types are listed as c, d, i, n, p, string, t, and x.

Fixed length built-in numeric types are :
I ABAP Type: i numeric type is used for integer or for whole numbers in 4 bytes length.
F ABAP Type: f numeric type is used for floating point number and is in 8 bytes length.
P ABAP Type: p numeric data type is used for packed number and is in 8 bytes length by default.

Fixed length built-in character types are :
C ABAP Type: c character type is used for text fieldsand is in 1 bytes length by default.
D ABAP Type: d character type is used for date fieldsand is 8 bytes length.
N ABAP Type: n character type is used for numeric text fieldsand is in 1 bytes length by default.
T ABAP Type: t character type is used for formatand is in 6 bytes.

Fixed length built-in hexadecimal type is :
X ABAP Type: x character type is used for hexadecimal fieldand is in 1 bytes length by default.

Variable length predefined ABAP data types are :
STRING ABAP Type: string character type is used for string variables.
XSTRING ABAP Type: xstring character data type is used for byte string variables and contains hexadecimal type value in it.