Updated code for more compliance

Made a lot of changes to the code:

1. clrscr() non-standard. Switched from clrscr() -> system("cls");
2. void main() is non-standard. Switched from void main() -> int main()
3. Removed redundant imports (conio.h)
4. Removed if statements in gridChar(). Switch is faster than
if/then/else since compiler makes jump tables to optimize the branching.
5. Why read something when you want to ignore input? Removed getch()
(non-standard) and replaced it with std::cin.ignore();
6. Switched to scanf calls for performance improvements
7. Switched to 1D/2D STL vectors [w/ initializer lists] instead of 1D/2D
arrays (note: requires a C++ 11 compliant compiler)
8. Properly declared integers as signed or unsigned as per requirements
in code
9. Fixed tabs
10. Appended std:: to iostream calls