What is operator promotion?


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 - 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 variablef2 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 <stdio.h>
    float f1 = 3 / 4;
    float f2 = 3 / 4.0;
    printf("3 / 4 == %g or %g depending on the type used.\n", f1, f2);


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