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# proj() function for Complex Numbers in C++

• Last Updated : 05 Aug, 2021

The proj() function is a built-in function and is defined in the complex header file. This function is used to find the projection of complex number onto the Riemann sphere.
Syntax:

```template <class T> complex<T>
proj (const complex<T>& z);```

Parameter:

• z: This method takes a mandatory parameter z which represents the complex number.

Return value: This function returns the projection of complex number z onto the Riemann sphere.
Below programs illustrate the proj() function in C++:
Example 1:

## CPP

 `// C++ program to demonstrate``// example of proj() function` `#include ``using` `namespace` `std;` `int` `main()``{``    ``// defines the complex number: (2 + 2i)``    ``complex<``double``> complexnumber(2, 2);` `    ``cout << ``"proj"` `<< complexnumber << ``" = "``                   ``<< proj(complexnumber) << endl;` `    ``return` `0;``}`
Output:
`proj(2,2) = (2,2)`

Example 2:

## CPP

 `// C++ program to demonstrate``// example of proj() function.` `#include ``using` `namespace` `std;` `int` `main()``{``    ``complex<``double``> complexnumber(INFINITY, -2);` `    ``cout << ``"proj"` `<< complexnumber << ``" = "``                   ``<< proj(complexnumber) << endl;` `    ``return` `0;``}`
Output:
`proj(inf,-2) = (inf,-0)`

Example 3:

## CPP

 `// C++ program to demonstrate``// example of proj() function.` `#include ``using` `namespace` `std;` `int` `main()``{``    ``complex<``double``> complexnumber(2, -INFINITY);` `    ``cout << ``"proj"` `<< complexnumber << ``" = "``                   ``<< proj(complexnumber) << endl;` `    ``return` `0;``}`
Output:
`proj(2,-inf) = (inf,-0)`

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