double number = 512;
double logBase = 8;
double result = log(number) / log(logBase);
//result is 3
//natural logarithm and base 2 have their own functions
double ln = log(M_E);
//ln is 1
double result2 = log2(number);
//result2 is 9
printf("result is %g\n", result);
printf("ln is %g\n", ln);
printf("result2 is %g\n", result2);