Weird error - What does it mean / how to fix?

[mwell008]

I'm working on a lab for an introductory C++ course (we've learned strings, chars, cmath, if and if-else, for and while loops, and we just learned functions) and I tested my code (using cloud 9 as our IDE) and it worked fine but when I submitted it to our course submission size (zyBooks) I got some errors that I don't understand.

Our assignment is the follow: Write a program that simulates flipping a coin to make decisions. The input is how many decisions are needed, and the output is either heads or tails. Assume the input is a value greater than 0. For reproducibility needed for auto-grading, seed the program with a value of 2. In a real program, you would seed with the current time, in which case every program runs output would be different, which is what is desired but can't be auto-graded.

Your program must define and call a function: string HeadsOrTails() that returns "heads" or "tails".

NOTE: A common student mistake is to call srand() before each call to rand(). But seeding should only be done once, at the start of the program, after which rand() can be called any number of times.

  #include <iostream>
#include <cstdlib>
using namespace std;

string HeadsOrTails(int iterations) {
    int randomValue;
    string decision = "";
    int i;
    
    srand(2);
    
    for (i = 0; i < iterations; ++i) {
        randomValue = rand() % 2;
        
        if (randomValue == 0) {
            decision.append("heads\n");
        }
        else {
            decision.append("tails\n");
        }
    }
    
    return decision;
}

int main () {
    
    int numberOfDecisions;
    cin >> numberOfDecisions;
    
    cout << HeadsOrTails(numberOfDecisions);
    
    return 0;
}

Should I not have had HeadsOrTails do the loop, but rather have the loop in main and it runs the HeadsOrTails function as many times as was asked by the user?

[mwell008]

Forgot to include my error. Here it is:

main.cpp: In function ‘bool testPassed()’:
main.cpp:46:37: error: too few arguments to function ‘std::__cxx11::string HeadsOrTails(int)’
studentResult += HeadsOrTails();
^
main.cpp:6:8: note: declared here
string HeadsOrTails(int iterations) {
^~~~~~~~~~~~

[mwell008]

Okay, I change my code to do the loop in main rather than within HeadsOrTails and it worked.

New code:

string HeadsOrTails() {
    int randomValue;
    string decision;
    
    randomValue = rand() % 2;
    
    if (randomValue == 0) {
        decision = "heads";
    }
    else {
        decision = "tails";
    }
    
    return decision;
}

int main () {
    
    int numberOfDecisions;
    cin >> numberOfDecisions;
    
    int i;
    
    srand(2);
    
    for (i = 0; i < numberOfDecisions; ++i) {
        cout << HeadsOrTails() << endl;
    }
    
    return 0;
}

[E0p9LyTq]

Your error is because you forgot to include the <string> header in your first code example.

#include <iostream>
#include <cstdlib>
#include <string>

std::string HeadsOrTails(int iterations)
{
   std::string decision = "";

   for (int i = 0; i < iterations; ++i)
   {
      int randomValue = rand() % 2;

      if (randomValue == 0)
      {
         decision.append("heads\n");
      }
      else
      {
         decision.append("tails\n");
      }
   }

   return decision;
}

int main()
{
   srand(2);

   std::cout << "Number of coin flips: ";
   int numberOfDecisions;
   std::cin >> numberOfDecisions;

   std::cout << '\n' << HeadsOrTails(numberOfDecisions);

   return 0;
}

[zaphraud]

random numbers need to be completely not random in order to grade the random number assignments effortlessly by machine.

wouldn't want to risk being accused of bias by actually grading papers, after all.

what a total failure of the university system.

oh well.

[E0p9LyTq]

random numbers need to be completely not random in order to grade the random number assignments effortlessly by machine.

Already half-way there using rand/srand[/tt instead of the C++ [tt]<random> library.

Instructors who continue to teach outdated non-C++ methodology sure aren't doing their students any favors.

[jonnin]

reseeding isnt always a mistake, sometimes you want to regenerate the same values as before for whatever reason. You can exploit the reseeding to do that. When done on purpose, its useful, and not an error. In general, seed once is correct. The reason you are allowed to seed it is so you can repeat the same values, its a feature to use when you need that.