definition-of-data-type.txt

Dan Saks

what is a data type?

A data type is a bundle of compile-time properties for an object:

1- size and alignment
2- set of valid values
3- set of permitted operations

Example:

type int:
1- size and alignment of 4 bytes
2- values from -2147483648 to 2147483647, inclusive
    integers only
3- operations including
    unary +, -, !, ~, &, ++, --
    binary =, +, -, *, /, %, <, >, ==, !=, &, |, &&, ||

What a type can't do is also important:
an int can't do

*i    // indirection
i.m   // member selection
i()   // call 

A type's operations my include implicit type conversion to other types. 
These conversion rules can be valid or invalid and be checked at compile time.

Strong typing prevents bad bugs caused by accidents:
int *p, *q;
double x, y;
p = q /4;     // error can't use divide operator on pointers
x = y & 0xFF; // error: can't bitwise-AND a double