CS156: Intro to C, Part I
Spring 2018
Float Vs Double
float and double are both floating-point types
float generally has less precision than double
float f = 1.0e9; double d = 1.0e9; f += 123.456789; d += 123.456789; printf("%f\n", f); printf("%f\n", d);
1000000128.000000 1000000123.456789
Calculations are generally carried out with double precision.
float f = 1.0e9; double d = f + 123.456789; printf("%f\n", d);
1000000123.456789
f + 123.456789 must have used double precision.
scanf needs to know the difference between float and double:
float f; double d; scanf("%f %lf", &f, &d);
float, use %f.
double, use %lf (think “long float”).
float expressions are evaluated using
double precision?
float arguments to functions are promoted to double.
printf can’t tell the difference between a
float and a double argument.
%f and %lf work for both float and double
in printf.
float f = 1.2; double d = 3.4; printf("%f\n", f); printf("%f\n", d); printf("%lf\n", f); printf("%lf\n", d);
1.200000 3.400000 1.200000 3.400000
