Project Euler: http://projecteuler.net/

ProjectEuler/p002_EvenFibNum.cpp

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+/* Check cf5-opt.vim defs.
+VIM: let g:lcppflags="-std=c++11 -O2 -pthread"
+VIM: let g:wcppflags="/O2 /EHsc /DWIN32"
+*/
+#include <iostream>
+
+/*
+Even Fibonacci numbers
+Problem 2
+Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
+
+1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
+
+By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.
+
+Solution:
+4613732
+*/
+
+int main ( void )
+{
+
+	int x = 1;
+	int y = 2;
+	int z = x+y;
+	int s = 0;
+	while ( z < 4000000 )
+	{
+		s+= z;
+		x = y;
+		y = z;
+		z = x+y;
+	}
+	if ( y%2 )
+	{
+		s -= y;
+		if ( x%2 )
+			s -= x;
+	}
+	s /= 2;
+	s += 2;
+	std::cout << s << std::endl;
+
+	return 0;
+}
+