Using arithmetic operators is the basic, essential way in which you can manipulate variables. C++ lets you add, subtract, multiply, divide, and compute the modulo, given two or more numbers (which are usually expressed as variables). For more complicated expressions, parentheses are useful for clarifying the order of evaluation. To increase or decrease a variable's value by a certain amount, there are special operators that allow modification. These include operators like *= ("multiply-by") and ++, the increment operator, which may be used before or after the variable name depending on the desired order of operation.
No programming language can be entirely useful without the means for some kind of input and output. C++'s iostream.h header file contains the convenient cout and cin operators for outputting information and reading input, respectively. The cout command uses the << operator followed by the output, while cin uses the >> operator to take user input. Outputting endl moves to the next line and flushes the output stream, which basically means that anything the computer was "waiting" to output is finally displayed.
If/else-statements and switch-statements carry out commands if and only if certain conditions are met. If/else-statements test a condition by using logical operators, and if the condition evaluates to a logical true, a specified block of code is executed. If the condition is false and there is an else block, it is executed. Switch statements act based on the value of a single variable; depending on the variable's value, the program will execute different segments of code.
Loops repeatedly execute a block of code until some condition is reached or the loop is told to break. There are 3 kinds of loops in C++: for-loops, while-loops, and do-loops. For-loops include the option of initializing a counter variable to some value, and a way of incrementing this (or another) value at the end of every pass through the loop. While-loops simply loops while a specified test condition is true, and do-loops are while loops that are guaranteed to make at least one pass through the loop.