The representations and sets of values of the various types of floating-point numbers (§3.1.2.5)
The float type contains 32 bits: 1 for the sign, 8 for the exponent, and 23 for the mantissa. Its range is +/– 3.4E38 with at least 7 digits of precision.
The double type contains 64 bits: 1 for the sign, 11 for the exponent, and 52 for the mantissa. Its range is +/– 1.7E308 with at least 15 digits of precision.
The long double type is new to Version 7.0 of Microsoft C. It contains 80
bits: 1 for the sign, 15 for the exponent, and 64 for the mantissa. Its range is
+/– 1.2E4932 with at least 17 digits of precision.