Question

In C, what is the difference between these two?

float myF = 5.6;

printf( "%i \n", (int)myF ); // gives me "5"
printf( "%ld \n", floor(myF) ); // also "5"?

When is one preferable over the other?

Answer 1

One big difference is that of negative numbers; if you change myF to -5.6, then casting to an int returns -5 while floor(myF) is -6.

As to which is preferable, as a rule of thumb I’d say to only cast to an int if you know that’s what you need — and since you’re asking here, chances are that you probably want floor.

(Also note that with printf formatting, %ld is a long integer; a double is %lf.)