Just assuming that your division should result in a fraction in normal math won't magically make it a float.
int a = 9/5;
You need to use
float a = 9.0/5;
First you need the right data type i.e. float (or better yet double for higher precision) to store a float.
Secondly, if you are dividing two integers i.e. 9 and 5, it will simply follow integer division i.e. only store the integer part of division and discard the rest. To avoid that i have added .0 after 9. This would force compiler to implicitly covert into float and do the division.
Regarding your mentioning of why it is printing 0, it is already mentioned that trying %f on integer is undefined behavior. Technically, a float is 4 bytes containing 3 byte number and 1 byte exponent and these are combined to generate the resultant value.
