Logical expressions

There is no boolean type in C (you cannot declare a variable to be boolean, or return a boolean from a function), but it does have a notion of a logical expression usually found in if, for and while statements.

if (a == 1) { /* .. */ } while (row < n_rows) { /* .. */ }

Such expressions are normally formed using one of the comparison operators (<, <=, == (equality) != (non-equality), >= and >). In fact, if e is an arbitrary expression which is to be interpreted as true of false, C will treat the expression as e!=0 if e is a numeric type

if (a) { /* do something */ }

will be interpreted as

if (a != 0) { /* so something */ }

C will convert from a logical expression to a numerical type automatically using the convention: true becomes 1 (or 1.0 for floating-point types), false becomes 0 (or 0.0). Combined with the behavior described above, you can use any numerical type as if it were boolean, with the interpretation zero=false, non-zero=true.

int a; /* we'll use this as if it were boolean */ a = (1<2); /* assigns 1 to a because the expression is true */

(CCATSL defines a boolean type and boolean constants true and false.)