How a program works in C++

4 minutes

Let's briefly go over the terms and syntax you used in the Hello World program. Breaking down the syntax can give you insight into the concepts behind the language and its structure.

Syntax breakdown

To better understand what's going on, it's helpful to go through the syntax of the program line by line, starting at the top row:

#include <iostream>: iostream is part of a standard library. Many components in a program are defined either by standard libraries or by libraries that you or a third party writes. The code uses iostream, which is part of a standard library, to use the object cout to print something as output.
```
#include <iostream>
```
using namespace std;: A namespace helps prevent name conflicts in large projects. You want to use the functionalities of a namespace throughout the code without repeatedly calling the namespace when it's required. So, you declare the namespace at the beginning of the code. Also, the syntax that's required for using cout is std::cout. By adding the line using namespace std;, you don't need to repetitively use std.
```
#include <iostream>
using namespace std;
```
int main(): A function is a set of statements that perform a task together. main() is a global function and the designated start of a program. Every C++ program has a mandatory main() function. The int used before main() says that this function expects an integer to be returned.
```
#include <iostream>
using namespace std;
int main() 
{
  cout << "Hello World\n";
  return 0;
}
```
cout: cout prints a specific string as output. std::cout is part of a collection of data and operations of the std::ostream class.
```
#include <iostream>
using namespace std;
int main() 
{
  cout << "Hello World\n";
  return 0;
}
```
"Hello World": The output Hello World is set in double quotes (""). You can use std::string in many ways. The main two ways to use std::string are as a C-string (character array) or as a string class. char is a primitive data type.

We use different data types, like integer, float, double, and char, to express and store values. For example, an integer might be 123, a float might be 9.02, and a char might be 'a'.
\n: Use \n to terminate the string and move to the next line. \n is called an escape sequence.
return 0: When you declare the int main() function, you specify int to declare the function, which returns an integer. If the function is preceded by int, it expects an integer in the return. By using return 0, you make sure that an integer is returned to complete the function. Here, return is the keyword and 0 is the integer.
```
#include <iostream>
using namespace std;
int main() 
{
  cout << "Hello World\n";
  return 0;
}
```

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Syntax breakdown

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