Data Type Conversions 327Here’s a function called distancethat calculates the distance between two points.#include <math.h>
double distance (Point p1, Point p2)
{
double diffx, diffy;
diffx = p1.x - p2.x;
diffy = p1.y - p2.y;return sqrt (diffx diffx + diffy diffy);
}
As previously noted,sqrtis the square root function from the standard library. It is
declared in the system header file math.h, thus the reason for the #include.
Remember, the typedefstatement does not actually define a new type—only a new
type name. So the Countervariables jand n, as defined in the beginning of this section,
would in all respects be treated as normal intvariables by the C compiler.
Data Type Conversions
Chapter 4, “Variables, Data Types, and Arithmetic Expressions,” briefly addressed the fact
that sometimes conversions are implicitly made by the system when expressions are eval-
uated.The case you examined was with the data types floatand int.You saw how an
operation that involved a floatand an intwas carried out as a floating-point opera-
tion, the integer data item being automatically converted to floating point.
You have also seen how the type cast operator can be used to explicitly dictate a con-
version. So in the statement
average = (float) total / n;
the value of the variable totalis converted to type floatbefore the operation is per-
formed, thereby guaranteeing that the division will be carried out as a floating-point
operation.
The C compiler adheres to strict rules when it comes to evaluating expressions that
consist of different data types.
The following summarizes the order in which conversions take place in the evalua-
tion of two operands in an expression:
- If either operand is of type long double, the other is converted to long double,
and that is the type of the result. - If either operand is of type double, the other is converted to double, and that is
the type of the result. - If either operand is of type float, the other is converted to float, and that is the
type of the result.