C test exercise, variables negative conditional-CodePudding

The teacher said that whenever the c variable is negative then: "the variable a is negative", but this doesn't make sense.

Is the program written in the wrong form?

In my opinion else should be part of the if(a>0) with {}. I don t know why he chose to not use it.

In conclusion, is the correct form like: if(a>0){...}else and than cout?

#include <iostream>`

using namespace std;

int main(void) {

  int a, b, c;
  cin >> a;
  cin >> b;
  cin >> c;
  if (a > 0)
    if (b > 0)
      if (c > 0)
        cout << "they are all positive";
      else
        cout << "the number a is negative";
}

CodePudding user response：

Your teacher is correct. else applies to the newest if, so the value of c determines the output. (More specifically, the program will only print something when both a and b are positive.) You can test this by running the program.

The output "the number a is negative" is illogical, because that's the point of the test. The program is intentionally written incorrectly. If answers to all test questions were obvious, everybody would get the best grade.

CodePudding user response：

You need to use curly brackets otherwise else will only apply to the newest if. The program will only print when both a and b are positive.

CodePudding user response：

The core problem here is the lack of a clear specification of what the program is supposed to do. I suspect that you do have it, but without it available here I can only explain what the code is doing and how the quote from the teacher can be read as describing what the code does.

To visualise here is a modified version of your code, which is self-explaining (I hope):

#include <iostream>

using namespace std;

int main(void) {

  int a, b, c;
  cin >> a;
  cin >> b;
  cin >> c;
  if (a > 0)
    if (b > 0)
      if (c > 0)
        cout << "they are all positive"; // true
      else
        cout << "the number 'c'  is negative or zero, 'a' and 'b' are positive";
    else
      cout << "the number 'b'  is negative or zero , 'a' is positive, no idea about 'c'";
  else
    cout << "the number 'a'  is negative or zero , no idea about 'b' and 'c'";
        
}

I suspect that where this outputs "no idea" is where you might want to use more ifs, in order to describe the other numbers.

Note: I stuck to your style (without {}). But I recommend to use them generously. In my experience it makes life easier and in my opinion makes code more readable.

I think the quote from the teacher

whenever the c value is negative it say: " the a number is negative" but it doesn't make sense

Should be read as:

'Whenever the c value is negative (and the other two are positive) this code outputs: "the 'a' number is negative", but that doesn't make sense, because a is in fact positive when this output occurs.

And I agree.