What does this function expect to return? - c++

Question

Program specifies the following:
Write a program with total change amount as an integer input that outputs the change using the fewest coins, one coin type per line.
The coin types are dollars, quarters, dimes, nickels, and pennies.
Use singular and plural coin names as appropriate, like 1 penny vs. 2 pennies.
Your program must define and call the following function.
void ExactChange(int userTotal, vector& coinVals)
Positions 0-4 of coinVals should contain the number of dollars, quarters, dimes, nickels, and pennies, respectively.
My code is below:
#include <iostream>
#include <vector>
#include <sstream>
using namespace std;
/*
1) Write a program with total change amount as an integer input that outputs the change using the fewest coins, one coin type per line.
2) The coin types are dollars, quarters, dimes, nickels, and pennies.
3) Use singular and plural coin names as appropriate, like 1 penny vs. 2 pennies.
4) Your program must define and call the following function.
void ExactChange(int userTotal, vector<int>& coinVals)
5) Positions 0-4 of coinVals should contain the number of dollars, quarters, dimes, nickels, and pennies, respectively.
*/
void ExactChange(int userTotal, vector<int>& coinVals);
const int PENNIES_IN_DOLLAR = 100, PENNIES_IN_QUARTER = 25, PENNIES_IN_DIME = 10, PENNIES_IN_NICKEL = 5;
int main() {
int userTotal, changeRemaining;
cin >> userTotal;
changeRemaining = userTotal;
int dollars = changeRemaining / PENNIES_IN_DOLLAR;
changeRemaining = changeRemaining % PENNIES_IN_DOLLAR;
int quarters = changeRemaining / PENNIES_IN_QUARTER;
changeRemaining = changeRemaining % PENNIES_IN_QUARTER;
int dimes = changeRemaining / PENNIES_IN_DIME;
changeRemaining = changeRemaining % PENNIES_IN_DIME;
int nickels = changeRemaining / PENNIES_IN_NICKEL;
changeRemaining = changeRemaining % PENNIES_IN_NICKEL;
int pennies = changeRemaining;
vector<int> changeAmount;
vector<int> coinVals{dollars, quarters, dimes, nickels, pennies};
changeAmount = coinVals;
ExactChange(userTotal, changeAmount);
return 0;
}
void ExactChange(int userTotal, vector<int>& coinVals) {
if (userTotal == 0) {
cout << "no change" << endl;
}
if(coinVals.at(0) > 0) {
cout << coinVals.at(0);
if(coinVals.at(0) > 1) {
cout << " dollars" << endl;
}else {
cout << " dollar" << endl;
}
}
if(coinVals.at(1) > 0) {
cout << coinVals.at(1);
if(coinVals.at(1) > 1) {
cout << " quarters" << endl;
} else {
cout << " quarter" << endl;
}
}
if(coinVals.at(2) > 0) {
cout << coinVals.at(2);
if(coinVals.at(2) > 1) {
cout << " dimes" << endl;
}else {
cout << " dime" << endl;
}
}
if(coinVals.at(3) > 0) {
cout << coinVals.at(3);
if(coinVals.at(3) > 1) {
cout << " nickels" << endl;
}else {
cout << " nickel" << endl;
}
}
if(coinVals.at(4) > 0) {
cout << coinVals.at(4);
if(coinVals.at(4) > 1) {
cout << " pennies" << endl;
}else {
cout << " penny" << endl;
}
}
}
However, zybooks, the site where our college course does our labs gives me these messages indicating some problem with my code:
My question is, what do those "messages" mean? Any how could I fix the issues? It seems to me they are saying the function is outputting something incorrectly given a certain input, however, they also don't give me a correct output to compare to.

Answer 1

Your code is taking user input, converting it manually directly in main() before calling ExactChange(), and then passing the result of that conversion to ExactChange() for it to display as-is.
The way I read the instructions, and the way the screenshot shows the tests being performed, it is more likely that ExactChange() is expected to take user input and convert it onto a vector of coin amounts as output.
That would be consistent with the fact that ExactChange() takes a vector by non-const reference, which means it can freely modify the contents of the vector. If ExactChange() were meant for text output, it would make more sense for it to take the vector by const reference instead, so that it can't modify the vector, only view it.
If so, then it makes sense that your program would pass tests that give it user-defined input and look for specific text results, but your program would fail tests that execute ExactChange() directly with specific inputs and look for specific vector outputs. That is the whole point of Unit Tests - to test functions directly for expected behaviors, not test whole programs.
Your code likely needs to look more like the following instead:
#include <iostream>
#include <vector>
#include <sstream>
using namespace std;
/*
1) Write a program with total change amount as an integer input that outputs the change using the fewest coins, one coin type per line.
2) The coin types are dollars, quarters, dimes, nickels, and pennies.
3) Use singular and plural coin names as appropriate, like 1 penny vs. 2 pennies.
4) Your program must define and call the following function.
void ExactChange(int userTotal, vector<int>& coinVals)
5) Positions 0-4 of coinVals should contain the number of dollars, quarters, dimes, nickels, and pennies, respectively.
*/
void ExactChange(int userTotal, vector<int>& coinVals);
const int PENNIES_IN_DOLLAR = 100, PENNIES_IN_QUARTER = 25, PENNIES_IN_DIME = 10, PENNIES_IN_NICKEL = 5;
int main() {
int userTotal;
cin >> userTotal;
if (userTotal == 0) {
cout << "no change" << endl;
}
else {
vector<int> coinVals;
ExactChange(userTotal, coinVals);
if (coinVals[0] > 0) {
cout << coinVals[0];
if (coinVals[0] > 1) {
cout << " dollars" << endl;
} else {
cout << " dollar" << endl;
}
}
if (coinVals[1] > 0) {
cout << coinVals[1];
if (coinVals[1] > 1) {
cout << " quarters" << endl;
} else {
cout << " quarter" << endl;
}
}
if (coinVals.at(2) > 0) {
cout << coinVals[2];
if (coinVals[2] > 1) {
cout << " dimes" << endl;
}else {
cout << " dime" << endl;
}
}
if (coinVals[3] > 0) {
cout << coinVals[3];
if (coinVals[3] > 1) {
cout << " nickels" << endl;
}else {
cout << " nickel" << endl;
}
}
if (coinVals[4] > 0) {
cout << coinVals[4];
if (coinVals[4] > 1) {
cout << " pennies" << endl;
}else {
cout << " penny" << endl;
}
}
}
return 0;
}
void ExactChange(int userTotal, vector<int>& coinVals) {
int dollars = userTotal / PENNIES_IN_DOLLAR;
userTotal %= PENNIES_IN_DOLLAR;
int quarters = userTotal / PENNIES_IN_QUARTER;
userTotal %= PENNIES_IN_QUARTER;
int dimes = userTotal / PENNIES_IN_DIME;
userTotal %= PENNIES_IN_DIME;
int nickels = userTotal / PENNIES_IN_NICKEL;
userTotal %= PENNIES_IN_NICKEL;
int pennies = userTotal;
coinVals.resize(5);
coinVals[0] = dollars;
coinVals[1] = quarters;
coinVals[2] = dimes;
coinVals[3] = nickels;
coinVals[4] = pennies;
}

Answer 2

I agree with Remy. An easier way of saying it would be that Zybooks sets the size for the vector as you open the section:
vector<int> changeAmount(5);
To pass the two problems, instead of clearing out the (5) or push_back'ing the amounts (which is 100% what I originally did), you just need to point the coin amount to the already created vector index directly.
Your code did this:
vector<int> coinVals{dollars, quarters, dimes, nickels, pennies};
changeAmount = coinVals;
When all you needed to do for each amount was:
coinVals.at(3) = dollars;
Because the vector is pass by reference (that '&' right before the vector name), your updates to the vector will be carried back through to your main function.
Thanks for posting! This thread helped me solve this one as well!