تفاوت ارسال پارامترهای تابع به صورت مقدار، ارجاع و اشاره گر

 
int increase(int x, int count = 1) // count variable has a default value: 1
{
   x += count; // The copy of x will be changed, not the orginal x sent from caller
   return x;
}
int main(int argc, char* argv[])
{
   int i = 10;
   int j = increase(i, 5); // The first parameter is a variable and the second is a constant
   cout << "i = " << i << "\n"; // i = 10
   cout << "j = " << j << "\n"; // j = 15
 
   j = increase(10, 5); // Both parameters are constant! 
   cout << "j = " << j << "\n"; // j = 15
   return 0;
}
 

 
int increase(int &x, int count = 1) // The first parameter is declared by reference, but the second is declared by value
{
   x += count;
   return x;
}
 
int main(int argc, char* argv[])
{
   int i = 10;
   int j = increase(i, 5);
   cout << "i = " << i << "\n"; // i = 15
   cout << "j = " << j << "\n"; // j = 15
 
   j = increase(10, 5); //WRONG, since the first parameter can not be constant
 
   return 0;
}
 

 
int increase(int *x, int count = 1) // The first parameter is declared as a pointer
{
   (*x) += count;
   return x;
}
 
int main(int argc, char* argv[])
{
   int i = 10;
   int j = increase(&i, 5); 
   cout << "i = " << i << "\n"; // i = 15
   cout << "j = " << j << "\n"; // j = 15
   return 0;
}
 

 
int StdDev(double* pData, int len, double* pMean, double* pStdDev)
{
   if( !pData || !pMean || (len < 1) ) return -1; // Indicate an error
   *pMean = 0;
   for (int i = 0; i < len; i++) 
      *pMean += pData[i];
   *pMean /= (double)len;
   if(! pStdDev) return -2; // Indicate another error 
   *pStdDev = 0;
   if(len < 2) return 0; // No Error
 
   for(int i = 0; i < len; i++) 
      (*pStdDev) += (pData[i] - (*pMean)) * (pData[i] - (*pMean));
 
   *pStdDev = sqrt( (*pStdDev) / (len - 1) );
   return 0;
}