Boolean Data Type - C, C++, Objective-C, Awk, Perl, Python

C, C++, Objective-C, Awk, Perl, Python

The initial implementations of the C language (1972) provided no Boolean type, and to this day Boolean values are commonly represented by integers (ints) in C programs. The comparison operators ('>', '==', etc.) are defined to return a signed integer (int) result, either zero (for false) or 1 (for true). The same convention is assumed by the logical operators ('&&', '||', '!', etc.) and condition-testing statements ('if', 'while').

After enumerated types (enums) were added to the ANSI version of C (1989), many C programmers got used to defining their own Boolean types as such, for readability reasons. However, enumerated types are equivalent to integers according to the language standards; so the effective identity between Booleans and integers is still valid for C programs.

Standard C (since C99) and several dialects of C such as and Objective-C provide definitions of a Boolean type as an integer type and macros for "false" and "true" as 0 and 1, respectively. Thus logical values can be stored in integer variables, and used anywhere integers would be valid, including in indexing, arithmetic, parsing, and formatting. This approach ("Boolean values are just integers") has been retained in all later versions of C.

C++ has a separate Boolean data type ('bool'), but with automatic conversions from scalar and pointer values that are very similar to those of C. This approach was adopted also by many later languages, especially by some scripting ones such as AWK and Perl. One problem with this approach is that the tests if(t==TRUE){...} and if(t) are not equivalent. Python has a related situation, where the Boolean type, bool is a subtype of the integer type, int, and Booleans False and True act as 0 and 1, respectively, in arithmetic contexts.