How to extract the decimal part from a floating point number in C?

Question

How can we extract the decimal part of a floating point number and store the decimal part and the integer part into two separate integer variables?

Solution 1

You use the modf function:

double integral;
double fractional = modf(some_double, &integral);

You can also cast it to an integer, but be warned you may overflow the integer. The result is not predictable then.

Solution 2

Try this:

int main() {
  double num = 23.345;
  int intpart = (int)num;
  double decpart = num - intpart;
  printf("Num = %f, intpart = %d, decpart = %f\n", num, intpart, decpart);
}

For me, it produces:

Num = 23.345000, intpart = 23, decpart = 0.345000

Which appears to be what you're asking for.

Solution 3

The quick "in a nut shell" most obvious answer seems like:

#define N_DECIMAL_POINTS_PRECISION (1000) // n = 3. Three decimal points.

float f = 123.456;
int integerPart = (int)f;
int decimalPart = ((int)(f*N_DECIMAL_POINTS_PRECISION)%N_DECIMAL_POINTS_PRECISION);

You would change how many decimal points you want by changing the N_DECIMAL_POINTS_PRECISION to suit your needs.

Solution 4

Use the floating number to subtract the floored value to get its fractional part:

double fractional = some_double - floor(some_double);

This prevents the typecasting to an integer, which may cause overflow if the floating number is very large that an integer value could not even contain it.

Also for negative values, this code gives you the positive fractional part of the floating number since floor() computes the largest integer value not greater than the input value.

Solution 5

I created a subroutine one using a double float, it returns 2 integer values.

void double2Ints(double f, int p, int *i, int *d)
{ 
  // f = float, p=decimal precision, i=integer, d=decimal
  int   li; 
  int   prec=1;

  for(int x=p;x>0;x--) 
  {
    prec*=10;
  };  // same as power(10,p)

  li = (int) f;              // get integer part
  *d = (int) ((f-li)*prec);  // get decimal part
  *i = li;
}

void test()
{ 
  double df = 3.14159265;
  int   i,d;
  for(int p=2;p<9;p++)
  {
    double2Ints(df, p, &i,&d); printf("d2i (%d) %f = %d.%d\r\n",p, df,i,d);
  }
}

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