phi value c++ inbuilt function code example

Example: euler's totient function c++

// C program to calculate Euler's Totient Function 
#include <stdio.h> 

int phi(int n) 
{ 
	int result = n; // Initialize result as n 

	// Consider all prime factors of n and subtract their 
	// multiples from result 
	for (int p = 2; p * p <= n; ++p) { 
		
		// Check if p is a prime factor. 
		if (n % p == 0) { 
			
			// If yes, then update n and result 
			while (n % p == 0) 
				n /= p; 
			result -= result / p; 
		} 
	} 

	// If n has a prime factor greater than sqrt(n) 
	// (There can be at-most one such prime factor) 
	if (n > 1) 
		result -= result / n; 
	return result; 
} 

// Driver program to test above function 
int main() 
{ 
	int n; 
	for (n = 1; n <= 10; n++) 
		printf("phi(%d) = %d\n", n, phi(n)); 
	return 0; 
}