#include <iostream> lets the compiler know about functions from the iostream header. Header files provide a list of the funtions and variables from other source files. You can think of them as a code equivalent of a table of contents in a book. The iostream header lets the compiler know about std::cout and std::endl. This std:: thing is there because most of the standard library is put into what's called a namespace. To get anything inside a namespace you have to preface the name of the variable/function with nameOfNamespace::. For all of the standard library, this would be std::. If you don't want to have to type std:: every time, you can instead use:
The as you can see above, to output anything, first use cout << followed by whatever text you would like to output. In addition, any extra << after will act as glue and stick "components" together. endl represents a newline "component". We could also just use "HelloWorld!\n" since \n represents a newline character, however, Windows uses \r\n and endl will automatically use the correct one.
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