4.1 An Example with Non-Integer Numbers

Here’s a function that operates on and returns floating point numbers that don’t have to be integers. Floating point represents a number as a fraction together with a power of 2. (For more detail, see Floating-Point Data Types.) This example calculates the average of three floating point numbers that are passed to it as arguments:

double
average_of_three (double a, double b, double c)
{
  return (a + b + c) / 3;
}

The values of the parameter a, b and c do not have to be integers, and even when they happen to be integers, most likely their average is not an integer.

double is the usual data type in C for calculations on floating-point numbers.

To print a double with printf, we must use ‘%f’ instead of ‘%d’:

printf ("Average is %f\n",
        average_of_three (1.1, 9.8, 3.62));

The code that calls printf must pass a double for printing with ‘%f’ and an int for printing with ‘%d’. If the argument has the wrong type, printf will produce meaningless output.

Here’s a complete program that computes the average of three specific numbers and prints the result:

double
average_of_three (double a, double b, double c)
{
  return (a + b + c) / 3;
}

int
main (void)
{
    printf ("Average is %f\n",
            average_of_three (1.1, 9.8, 3.62));
    return 0;
}

From now on we will not present examples of calls to main. Instead we encourage you to write them for yourself when you want to test executing some code.