c++ - What does access violation mean? -

i'm new c++ , not understand why getting error "access violation reading location". here code:

gdiscreen(); int startx = 1823 - minusx; int starty = 915 - minusy; (int = startx; < startx + 61; i++) {     (int j = starty; j < starty + 70; j++)     {         color pixelcolor;         bitmap->getpixel(i, j, &pixelcolor);         cout << pixelcolor.getvalue() << " ";     }     cout << endl; } 

gdiscreen() can found here: http://forums.codeguru.com/showthread.php?476912-gdi-screenshot-save-to-jpg

please help!!

access violation or segmentation fault means program tried access memory not reserved in scope.
have few examples how achieve this:

leaving bounds of array:

int arr[10]; for(unsigned char i=0; i<=10; i++)  //will throw error @ i=10     arr[i]=0; 

^{note: in code above, use unsigned char iterate. char 1 byte, unsigned char 0-255. larger numbers, may need unsigned short (2 bytes) or unsigned int (4 bytes).}

accidentally calculating pointer instead of integer

int ah = 10; int *pointer = &ah;   //for reason, need pointer pointer++;   //we should've written this: (*pointer)++ iterate value, not pointer std::cout<<"my number:"<<*pointer<<'\n';  //error - accessing ints address+1 

i intentionally started broad explanation. wanted know access violation @ first place. in particular code, i'm sure messed i , j boundaries. std::cout debug.