I cant understand what is wrong with I

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#include <iostream>
#include <string.h>
/*me thn xrhsh constructor emfanizw to onoma to am ton meso oro ton megisto kai ton elaxisto*/



using namespace std;

class Student
{
	private:
		string name;
		string am;
		int marks[50],avg,max,min, i;
	public:
		Student(string name, string am,  int avg, int max, int min):name(name), am(am), avg(avg), max(max), min(min)
		{
			
		 } 
  	string get_name() { return name; }
  	string get_am() { return am; }
	int get_avg() { return avg; }
	int get_max() { return max; }
	int get_min() { return min; }		
};

int main()
{
	  	string name, am;
  		int marks, avg, max, min, sum=0, mx, m, i;
  		
  			cout<<"Enter Name:";
			cin >>name;

			cout<<"Enter Am:";
			cin >>am;

			cout<<"Enter 5 marks:\n";
			min=marks[i];
			min=marks[i];
			for(i=0;i<5;i++)
			{
				do{
					cout<<"Give "<<i+1<<"o: ";
					cin>>marks[i];
				}while(marks[i]<0 || marks[i]>10);
				
				sum=sum+marks[i];
				
				if(mx<marks[i])
				{
					mx=marks[i];
				}
				if(m>marks[i])
				{
					m=marks[i];
				}													
			}
			
			avg=sum/5;
			max=mx;
			min=m;
			
			Student s(name, am, avg, max, min);
			
			cout<< s.get_name() << s.get_am() << s.get_avg() << s.get_max() << s.get_min() ;
  		
  		
}

What I have tried:

i dont know what to do "

[Error] invalid types 'int[int]' for array subscript

"

Posted 8-Jun-21 17:12pm

User 15142741

Updated 8-Jun-21 20:23pm

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Comments

Joe Woodbury 8-Jun-21 23:34pm

marks in main() is not an array.
i is undefined before the for loop; if marks was an array it too would be undefined.
mx and m are undefined.
Why have both max and mx and min and m?
Also note that in C++, you should define variables as close as possible to where they are used.
I also suggest gathering the marks, passing them to Student and have Student do the calculation (separating the interface from the rest.)

3 solutions

Solution 1

When you write a function, any variables you create locally "hide" those outside the function with the same name:

C++

int x = 666;
void foo()
   {
   cout << x << endl;
   }
void bar()
   {
   int x = 333;
   cout << x << endl;
   }
void main()
   {
   int x = 111;
   foo();
   bar();
   }

Will print

C++

666
333

because the bar function hides the external variable x, and so does the main function.

So your main function declares a new local variable called marks :

C++

int main()
{
	  	string name, am;
  		int marks, avg, max, min, sum=0, mx, m, i;

which "hides" the external one. All references to marks inside the main function will refer to the local version which is not an array.

Worse, you then start trying to use the data in it without actually filling it with anything so even if you remove the local definition, your code still won't work properly!

I think you need to sit down and think carefully about what you are trying to do before you leap into code - that shows all the hallmarks of "diving straight in and coding" before working out what you need to do!

Have a look here, it may help: How to Write Code to Solve a Problem, A Beginner's Guide[^]

Posted 8-Jun-21 18:43pm

OriginalGriff

Solution 2

You must understand the scope rules in C. Read this fine scope tutorial to fully understand the "hiding" effects.

Posted 8-Jun-21 20:19pm

KarstenK

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CPallini · Accepted Answer · 2021-06-08T20:23:00

Your code is using marks like an array, but you have declared it (single) int.
Do you realize you don't need an array at all?
Try

C++

class Student
{
  private:
    string name;
    string am;
    double avg;
    int max, min;
  public:
    Student(string name, string am,  double avg, int max, int min) : name(name), am(am), avg(avg), max(max), min(min)
    {
    }
    string get_name() { return name; }
    string get_am() { return am; }
    double get_avg() { return avg; }
    int get_max() { return max; }
    int get_min() { return min; }
};

int main()
{
  const int Items = 5;
  string name, am;
  int max, min, sum;
  double avg;

  cout<<"Enter Name:";
  cin >>name;

  cout<<"Enter Am:";
  cin >>am;

  cout<<"Enter " << Items << " marks:\n";
  sum = 0;
  min = 11;
  max = -1;

  for( int i=0; i<Items; i++ )
  {
    int marks;
    do
    {
      cout<<"Give "<<i+1<<"o: ";
      cin>>marks;
    } while ( marks < 0 || marks > 10);

    sum += marks;

    if ( max < marks)
      max = marks;

    if ( min > marks)
      min = marks;
  }
  avg = (double) sum / Items;

  Student st(name, am, avg, max, min);

  cout << st.get_name() << ", " <<  st.get_am() << ", " << st.get_avg() << ", " << st.get_max() << ", " <<  st.get_min() << endl;

}