#include <iostream>
#include <string>
 
using namespace std;
 
 
void det_max(int yards,int max)
{
        if (yards >= max)
                max = yards;
}
 
void showRByards(string playername, int weekno, int yards, int stars)
{
        cout << "Input a RB Name: (or type x to stop)" << playername <<
endl;
        cout << "Input Week  " << weekno <<"'s yardage : "<< yards <<
endl;
   cout << "Yards for the week: " << yards << endl;
 
        cout << playername << "'s rushing yardage for week " << weekno << ": " ;
        stars = yards/10;
        int j = 0;
        while (j<stars)
                {
                        cout << "*";
                        j++;
     }
        cout << endl;
}
int main ()
{
int max = 0;
int count = 0;
int weekno = 1;
 
string name;
string playername = " ";
 
// Variable for player names
 
int weeks, yards, stars;
 
cout << "Input the number of weeks: ";
cin >> weeks;
 
if (weeks>0 && weeks<7)
{
        while (playername != "x")
{
        cout << "Input the RB name (or type x to stop): ";
        cin >> playername;
        while (count<weeks)
        {
        count++;
        cout << "Input Week " <<weekno<<"'s yardage : ";
        cin >> yards;
 
        det_max(yards,max);
        showRByards(playername,weekno,yards,stars);
        weekno++;
}
}
        cout << playername<<"'s best week was with "<<max << "yards.";
}
else
    cout <<"Invalid number of weeks." <<endl;
return 0;
 
}

void det_max(int yards,int max)
{
        if (yards >= max)
                max = yards;
}

int det_max(int yards, int max)
{
   if(yards>=max)
      return max;
   else
     return yards;
}
...
int main()
{
...
max=det_max(yards,max);
...
}