If an operation is specified with operands of two different types, they are converted to the smallest type that can hold both values. The result has the same type as the two operands wind up having. To interpret the rules, read the following table from the top down, and stop at the first rule that applies.
If Either Operand Is And the Other Is Change Them To
long double any other type long double
double any smaller type double
float any smaller type float
unsigned long any integral type unsigned long
long unsigned > LONG_MAX unsigned long
long any smaller type long
unsigned any signed type unsigned
The following example code illustrates some cases of operator promotion. The variable f1 is set to 3 / 4.
Because both 3 and 4 are integers, integer division is performed, and the result is the integer 0. The variable f2 is set to 3 / 4.0. Because 4.0 is a float, the number 3 is converted to a float as well, and the result is the float 0.75.
#include
main()
{
float f1 = 3 / 4;
float f2 = 3 / 4.0;
printf(“3 / 4 == %g or %g depending on the type used.\n”,
f1, f2);
}
Reference:
II.11: Are there any problems with performing mathematical operations on different variable types?
II.13: When should a type cast be used?
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