added lambda example

lambda.cc

@@ -0,0 +1,17 @@
+#include <vector>
+#include <algorithm>
+#include <iostream>
+
+using namespace std;
+
+int main() {
+    vector<int> ints = {1, 2, 3, 4, 5, 6};
+    int total = 0;
+    for_each(begin(ints), end(ints), [&total](int x) {
+            total += x;
+    });
+    cout << "total: " << total << endl;
+    auto my_lambda_doubling_func = [&](int x) -> int { return x * 2; };
+    cout << my_lambda_doubling_func(total) << endl;
+    return 0;
+}