'float' vs. 'double' precision

Question

The code

float x  = 3.141592653589793238;
double z = 3.141592653589793238;
printf(\"x=%f\\n\", x);
printf(\"z=%f\\n\", z);
printf(\"x=%20.18f\\n\", x);
print         


        

Answer 1

Floating point numbers in C use IEEE 754 encoding.

This type of encoding uses a sign, a significand, and an exponent.

Because of this encoding, many numbers will have small changes to allow them to be stored.

Also, the number of significant digits can change slightly since it is a binary representation, not a decimal one.

Single precision (float) gives you 23 bits of significand, 8 bits of exponent, and 1 sign bit.

Double precision (double) gives you 52 bits of significand, 11 bits of exponent, and 1 sign bit.