UMBC CS 201, Fall 05

Mixing Types

Mixing types can lead to strange results.

Generally, if a binary operator is used on both an integer and a double, the integer is converted to a double and the result is a double. Why? For example:

Dividing a 9.0 by 4 gives the double value 2.25
Dividing 9 by 4 gives the integer value 2

But consider: /***************************************** Program: mix.c Author: Richard Chang Date: ? Revised by: Sue Bogar Date revised: 2/2/98 Section: 101 E-Mail: bogar@cs.umbc.edu This program illustrates possible problems when mixing floating-point and integer types *****************************************/ #include <stdio.h> int main() { double x ; int i ; /* A floating-point constant assigned to an integer variable*/ i = 2.7 ; printf("i = %d\n", i) ; /* An integer constant assigned to a double */ x = 3 + 4 ; printf("x = %f\n", x) ; /* Mixing doubles and integers results in a double */ printf("\n") ; printf("9.0/4.0: %f\n\n", 9.0/4.0) ; printf(" 9/4.0: %f\n\n", 9/4.0) ; printf(" 9.0/4: %f\n\n", 9.0/4) ; /* A nasty surprise, integer division */ printf("9/4 printed using %%f: %f\n\n", 9/4) ; /* More nasty surprises*/ x = 9/4 ; printf("9/4 assigned into a double and printed with %%f: %f\n\n", x) ; return 0; } Which results in:

i = 2
x = 7.000000

9.0/4.0: 2.250000

  9/4.0: 2.250000

  9.0/4: 2.250000

9/4 printed using %f: 0.000000

9/4 assigned into a double and printed with %f: 2.000000

Type casting

You can explicitly convert a value of an expression to a specific type via a type cast operator

( <type name> )

For example: int numerator, denominator; double quotient; /* these statements produce the desired affect */ quotient = numerator / (double) denominator; quotient = (double)numerator / denominator; /* but this one does not... why? */ quotient = (double)(numerator / denominator); where numerator and denominator are both integers and quotient is a double, casting one of the integer variables to a double prevents integer division and causes the answer to be a double, then assigns that answer into the variable quotient.

Sunday, 21-Aug-2005 09:53:19 EDT