Question

float f = 0.00f;
System.out.println(f);      

gives the output:

0.00

I’d like to format a number represented by a percentage to 2 decimal places. But the result should be a float and not a string.

e.g.

10.001 needs to be converted to 10.00
0.0 needs to be converted to 0.00
78.8  needs to be converted to 78.80 

The values thus formatted will be assigned to a float.. how would one accomplish this?

Answer 1

In the general case, you can’t do that. There’s no guarantee that a particular decimal value can be represented by a float that has only two digits right of the decimal.

A float is the wrong data type for this kind of precision. You need to use a decimal type or a scaled integer instead.

Assignment works the same way. If you assign the value 133.47 to a floating-point variable, your environment will assign the closest valid floating-point number to the variable. The closest valid floating-point number will probably not be 133.47.

You can compile and execute this program in C.

#include <stdio.h>

int main (void) {
  float r;
  r = 133.47;
  printf("%.2f, %f\n", r, r);
  return 0;
}

It prints these values on my system

$ ./a.out
133.47, 133.470001

Formatting to two decimal places changed the way ‘r’ looks, but it didn’t change its value. Your system will do floating-point arithmetic based on the actual value, not the formatted value. (Unless you also change the data type.)