Tracing through E01, question 9 – step 1// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main

Tracing through E01, question 9 – step 2// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main

7k

Tracing through E01, question 9 – step 3// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

7k

mysteryFunction()

Tracing through E01, question 9 – step 4// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

7k

mysteryFunction()

x

The address of k is copied into xSince an address is a pointer,and a pointer is an address,x now points to k.

Tracing through E01, question 9 – step 5// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

7k

mysteryFunction()

x

result

Tracing through E01, question 9 – step 6// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

7k

mysteryFunction()

x

7result

(*x) means dereference the pointer xto go to what it points to. That is, k.

Since (*x) is really k, the value of k,which is 7, gets copied into result.

Tracing through E01, question 9 – step 7// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

7k

mysteryFunction()

x

7 21result

result gets multiplied by 3,and 7 changes to 21

Tracing through E01, question 9 – step 8// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

7 21k

mysteryFunction()

x

21result

Now, (*x) is on the left hand side. (*x) dereferences the pointer x, follows the arrow to what is pointed to,which is k.

So (*x) on the left hand side,really means that we are assigning a new value to k.

Tracing through E01, question 9 – step 9// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

21k

mysteryFunction()

x

21result

When we reach the end of the function,the call frame, and all of its local variablesare popped off of the stack, and they go away.

Tracing through E01, question 9 – step 10// p02.cc P. Conrad, for CISC181 07S // Exam question for E01 #include <iostream> using namespace std; void mysteryFunction(int *x); int main() { int k = 7; mysteryFunction(&k); cout << k << endl; return 0; }

void mysteryFunction(int *x) { int result; result = (*x); result = result * 3; (*x) = result; }

main()

21k

We have returned from the function,and we print the answer, 21.