fix structure errors

project_cpp/functions.cpp

@@ -0,0 +1,19 @@
+#include <iostream>
+#include <math.h>
+
+int add (int a, int b) {
+    return a + b;
+}
+
+
+int multiple (int a, int b) {
+    return a * b;
+}
+
+int substraction (int a, int b) {
+    return a - b;
+}
+
+int devide (int a, int b) {
+    return round(a / b);
+}