C++ for Scientists - Technische Universität Dresden

20 CHAPTER 2. C++ BASICS
• std::cout and std::endl are defined in “iostream.” The former is an output stream that prints
text on the screen (unless it is redirected). With std::endl a line is terminated.
• The special operator≪ is used to pass objects to the output to an stream std::cout that is
to print it on that stream.
• The double quotes surround string constants, more precisely string literals. This is the
same as in C. For string manipulation, however, one should use C ++’s string class instead
of C’s cumbersome and error-prone functions.
• The expression 6 ∗ 7 is evaluated and a temporary integer is passed to std::cout. In C ++
everything has a type. Sometimes we as programmers have to declare the type and
sometimes the compiler deduces it for us. 6 and 7 are literal constants that have type int
and so has their product.
This was a lot of information for such a short program. So let us start step by step.
TODO: A little explanation how to compile and run it. For g++ and Visual Studio.
2.2 Variables
In contrast to most scripting languages C ++ is strongly typed, that is every variable has a type
and this type never change. A variable is declared by a statement TYPE varname. 1 Basic types
are int, unsigned int, long, float, double, char, and bool.
int integer1 = 2;
int integer2, integer3;
float pi = 3.14159;
char mycharacter = ’a’;
bool cmp = integer1 < pi;
Each statement has to be terminated by a “;”. In the following section, we show operations
that are often applied to integer and float types. In contrast to other languages like Python,
where ’ and ” is used for both characters and strings, C ++ distinguishes between the two of
them. The C ++ compiler considers ’a’ as the character ‘a’ (it has type char) and ”a” is the string
containing ‘a’ (it has type char[1]). If you are used to Python please pay attention to this.
Advise
Define variables right before using them the first time. This makes your
programs more readable when they grow long. It also allows the compiler to
use your memory more efficiently when you have nested scopes (more details
later). Old C versions required to define all variables at the beginning of a
function and several people stick to this till today. However, in C ++ it leads
generally to higher efficiency and more importantly to higher readability to
define variables as late as possible.
1 TODO: too simple, variable lists and in-place initialization is missing