last code

arrayRef.cpp

@@ -0,0 +1,21 @@
+#include <iostream>
+using namespace std;
+
+// write a function that doubles the elements in an array of ints
+
+void doubler(int arr[], int l){
+  for(int i=0; i<l; i++){
+    arr[i] = 2*arr[i];
+  }
+}
+
+int main(){
+ int myArr[5] = {0,1,2,3,4};
+  
+  doubler(myArr,5);
+
+  for(int i = 0; i < 5; i++){
+    cout << myArr[i] << endl;
+  }
+  return 0;
+}

arrayTheTruth.cpp

@@ -0,0 +1,13 @@
+#include <iostream>
+using namespace std;
+
+int main(){
+
+  int myArr[5] = {0,1,2,3,4};
+
+  cout << myArr << endl;
+  cout << *(myArr + 0) << endl; // myArr[0]
+  cout << *(myArr + 1) << endl; // myArr[1]
+  cout << *(myArr + 2) << endl; // myArr[2]
+  return 0;
+}

byRef.cpp

@@ -0,0 +1,22 @@
+#include <iostream>
+using namespace std;
+
+void howManyPets(string petType, int &numPets){
+  int temp =0;
+
+  cout << "How many " << petType << " do you have?" << endl;
+  cin >> temp;
+  // if we were doing error handling we'd put that here
+  numPets = numPets + temp;
+}
+
+int main(){
+  int totalPets = 0;
+
+  howManyPets("cats", totalPets);
+  howManyPets("dogs", totalPets);
+  howManyPets("chickens", totalPets);
+  
+  cout << "you have " << totalPets << " pets" << endl;
+  return 0;
+}

byVal.cpp

@@ -0,0 +1,24 @@
+#include <iostream>
+using namespace std;
+
+int howManyPets(string petType){
+  int temp =0;
+
+  cout << "How many " << petType << " do you have?" << endl;
+  cin >> temp;
+  // if we were doing error handling we'd put that here
+  return temp;
+}
+
+int main(){
+  int totalPets = 0;
+
+  // totalPets = totalPets + howManyPets("cats");
+  // totalPets = totalPets + howManyPets("dogs");
+  // totalPets = totalPets + howManyPets("chickens");
+
+  totalPets = howManyPets("cats") + howManyPets("dogs") + howManyPets("chickens");
+
+  cout << "you have " << totalPets << " pets" << endl;
+  return 0;
+}

rectRef.cpp

@@ -0,0 +1,36 @@
+#include <iostream>
+using namespace std;
+
+struct Rect {
+  int width;
+  int height;
+  int area;
+};
+
+Rect makeRect(int w, int h){
+  Rect rect;
+  rect.width = w;
+  rect.height = h;
+  rect.area = -1;
+  return rect;
+}
+
+int area(Rect &r){
+  if(r.area == -1){
+    cout << "Calculating area: " << endl;
+    r.area = r.width * r.height;
+  }
+  return r.area;
+}
+
+int main(){
+  Rect myRect = makeRect(10,20);
+
+  cout << myRect.width << endl;
+  cout << myRect.height << endl;
+
+  cout << "Area: " << area(myRect) << endl;
+  // assume a long time passes in the program
+  cout << "Area: " << area(myRect) << endl;
+  return 0;
+}