The same operations seem to work differently for larger and smaller values (I think the code below explains the question better than I could in words) I have calculated max and max3 in the same way except the values are different. Similarly I have calculated max2 and max4 the exact same way with different values. Yet the answer I'm getting is very different?:
#include <stdio.h>
#include <math.h>
int main(void)
{
// 86997171 / 48 = 1812441.0625
int max = ceil((float) 86997171 / 48);
float max2 = ((float) 86997171)/ 48;
printf("max = %i, max2 = %f\n", max, max2);
int max3 = ceil((float) 3 / 2);
float max4 = ((float) 3) / 2;
printf("ma3 = %i, max4 = %f\n", max3, max4);
}
Output:
max = 1812441, max2 = 1812441.000000
ma3 = 2, max4 = 1.500000
I was expecting max = 1812442, max2 = 1812441.062500 to be the output, since that's what it should be in principle. Now I don't know what to do
In C, float is a single-precision floating-point format, so it is usually 4 bytes (on most compilers), so its precision is around 6-9 significant digits, typically 7 digits.
Your number in question, 1812441.0625 has 11 digits, which don't fit in a float type.
You should use double instead, which in C is a double-precision floating-point format, so it is usually 8 bytes (on most compilers) so its precision is around 15-18 significant digits, typically 16 digits, and therefore can keep the precision of your number.
In fact, using double in this case gives:
max = 1812442, max2 = 1812441.062500
ma3 = 2, max4 = 1.500000
which is what you need.
Note that the precision of these types is explained here. It is far from the truth (as explained by the link), but it gives good perspective in your question.