How to write a RoundDown() function with loops, + - * / and % (modulo)?

Question

I was just thinking, if you only had loops, + - * / and % (modulo). Would it be possible to round a float number down to the next integer?
For example 278.791 to 278?

I've been thinking about that for a long time now, but still couldn't find a solution. Is it even possible?

Answer 1

In Python % works:

#!/usr/bin/python
x = 278.791
y = x - (x % 1)
print x, y

In C other methods must be used:

#include <stdio.h>
#include <math.h>
int main() {
    float x = 278.791;
    float y = fmod(x,1.0);
    printf("%f, %f\n", x, y);
    x = 278.791;
    y = x - (int)x;
    printf("%f, %f\n", x, y);
}