6.6 Numeric Comparisons

There are two kinds of comparison operators: equality and ordering. Equality comparisons test whether two expressions have the same value. The result is a truth value: a number that is 1 for “true” and 0 for “false.”

a == b   /* Test for equal.  */
a != b   /* Test for not equal.  */

The equality comparison is written == because plain = is the assignment operator.

Ordering comparisons test which operand is greater or less. Their results are truth values. These are the ordering comparisons of C:

a < b   /* Test for less-than.  */
a > b   /* Test for greater-than.  */
a <= b  /* Test for less-than-or-equal.  */
a >= b  /* Test for greater-than-or-equal.  */

For any integers a and b, exactly one of the comparisons a < b, a == b and a > b is true, just as in mathematics. However, if a and b are special floating point values (not ordinary numbers), all three can be false. See Special Floating-Point Values, and Invalid Optimizations.