Which variables should I typecast when doing math operations in C/C++?

Question

For example, when I\'m dividing two ints and want a float returned, I superstitiously write something like this:

int a = 2, b = 3;
float c = (float)a / (floa         


        

Answer 1

In general, if operands are of different types, the compiler will promote all to the largest or most precise type:

If one number is...   And the other is...    The compiler will promote to...
-------------------   -------------------    -------------------------------
char                  int                    int
signed                unsigned               unsigned
char or int           float                  float
float                 double                 double

Examples:

char       + int             ==> int
signed int + unsigned char   ==> unsigned int
float      + int             ==> float

Beware, though, that promotion occurs only as required for each intermediate calculation, so:

4.0 + 5/3  =  4.0 + 1 = 5.0

This is because the integer division is performed first, then the result is promoted to float for the addition.