On some (especially older) platforms (see the comments below) you might need to and then include the necessary header file: and the value of pi can be accessed via: In my math.h (2014) it is defined as: but check your math.h for more. An extract from the “old” math.h (in 2009): However: on newer platforms … Read more
As it is, both dimensions of your vector are 0. Instead, initialize the vector as this: This will give you a matrix of dimensions RR * CC with all elements set to 0.
The problem C++ includes useful generic functions like std::for_each and std::transform, which can be very handy. Unfortunately they can also be quite cumbersome to use, particularly if the functor you would like to apply is unique to the particular function. If you only use f once and in that specific place it seems overkill to … Read more
This line doesn’t do the right thing: You want to count by 32, that’s either or I strongly recommend making the numeric and character values match during your output. So change to
pow() in the cmath library. More info here. Don’t forget to put #include<cmath> at the top of the file.
One method would be to use the array to initialize the vector
This is not related to performance at all. But consider this: you are using two libraries called Foo and Bar: Everything works fine, and you can call Blah() from Foo and Quux() from Bar without problems. But one day you upgrade to a new version of Foo 2.0, which now offers a function called Quux(). … Read more
Huge difference. As the name implies, a double has 2x the precision of float[1]. In general a double has 15 decimal digits of precision, while float has 7. Here’s how the number of digits are calculated: double has 52 mantissa bits + 1 hidden bit: log(253)÷log(10) = 15.95 digits float has 23 mantissa bits + … Read more
C++11 introduces std::stoi (and variants for each numeric type) and std::to_string, the counterparts of the C atoi and itoa but expressed in term of std::string. is therefore the shortest way I can think of. You can even omit naming the type, using the auto keyword: Note: see [string.conversions] (21.5 in n3242)
In C++11 there are some nice new convert functions from std::string to a number type. So instead of you can use where str is your number as std::string. There are version for all flavours of numbers: long stol(string), float stof(string), double stod(string),… see http://en.cppreference.com/w/cpp/string/basic_string/stol