C++ log() and log10()

log (or written commonly as ln) has a great significance in the world of mathematics, however, for computer implementation on some specific cases, I am not sure which one is better.

Yesterday, I was trying to solve a problem from uva online judge where I needed to find log_ba, which is calculated as log(a) / log(b) in C++. However, doing so led to a "wrong answer". Then, just to check, rewrote that formula with an equivalent one using log10(a) / log10(b), and this time it worked fine. Really confusing, so I come to this conclusion, log (e based) is not quite precise on computer implementation, especially with gcc/g++. Because, both produces same output on my machine, but different in uva's gcc/g++ compiler. Any other reason?

A C++ Mistake

Consider this piece of code:

 int f = 10;  int ff() {     return f = 5; }  int main() {     printf("%d %d\n", ff(), f);     return 0; } 

As I have expected it to print "5 5" (I was using Dev C++) so did I get, but I didn't know it was wrong until the judge showed me the famous and fabulous "WA". The correct output is "5 10", because, function parameters are though of to be similar as assignment operation and should be performed from right to left. Now it makes sense. But got some penalty for stupid yet adorable Dev C++. However, I've learnt this... that's the good side of it! So, you too be careful if you don't know that already.