Nrthugu

I am new to Stack overflow and I am wondering if I can get help regarding my C++ code.

I want to fill my 2D array with the users input, for example:

• Please Enter 16 characters: (abcdabcdabcdabcd)

Outputs a 4x4 grid that is filled with user's input in this case its (abcdabcdabcdabcd).

a b c d

a b c d 

a b c d

a b c d

Here is my progress up till now:

#include <iostream>

#include <stdlib.h>



using namespace std;



//Constants

const int SM_GRID = 3;

const int LG_GRID = 4;

const char FILL_1 = 'X';

const char FILL_2 = 'O';

const int FORWARD = 1;

const int REVERSE = 2;

const int MAXLEN = 128;



//displays an overview of the program

void displayOverview();



//fills a small array with x's and o's

void fillSmallArray(char grid[SM_GRID]);



//prompts the user for characters, and fills a 4x4 array with them

//either fills it from top to bottom, left to right (if direction is 1)

//or bottom to top, right to left (if direction is 2)

void fillLgArray(char grid[LG_GRID], int direction);



//outputs the small array

void outputSmallArray(char grid[SM_GRID]);



//outputs the large array

void outputLgArray(char grid[LG_GRID]);



//prompts for a command, and calls the appropriate function based on it

//returns true if command was valid

bool doCommand(char grid[LG_GRID]);





int main(){



  //Overview of the program

  displayOverview();



  //set up arrays

  char myGrid[SM_GRID][SM_GRID];

  fillSmallArray (myGrid);

  outputSmallArray(myGrid);



  //declare a large array

  //declare variable: Play or Not?

  //As long as user wants to play

  //call doCommand

  char myGrid1[LG_GRID][LG_GRID];

  doCommand (myGrid1);



    //fill the small array and output it



    //fill the large array and output it, as many times as the user wants

    //1 for forward, 2 for reverse, any other character ends the game



return 0;

}





//displays an overview of the program

void displayOverview(){

  cout << "Welcome to my grid-o-matic game !! :)n"

  << "Here is your small grid: n";



}





//fills a small array with x's and o's

void fillSmallArray(char grid[SM_GRID]){

  //logic: if both row and col are even, or both odd, put in a X

  //otherwise put in a O

  //loop through the grid put in a X or O as above

  for (int row = 0; row < SM_GRID; row++){

    for(int col = 0; col < SM_GRID; col++){

      if((row %2) == (col%2)){

grid [row][col] = FILL_1;

      }else{

grid [row][col] = FILL_2;

      }//if else

    }//inner for

  }//outer for

}//function







//prompts the user for characters, and fills a 4x4 array with them

//either fills it from top to bottom, left to right (if direction is 1)

//or bottom to top, right to left (if direction is 2)



void fillLgArray(char grid[LG_GRID], int direction){





    string userInput;



    cout << "Please enter 16 characters!n";

    cin >> userInput;



    if(userInput.length() > 16){



        userInput = userInput.substr(0, 16);

    }



    cout << "You entered " << userInput << endl;



    for (int row = 0; row < LG_GRID; row++){

        for (int col = 0; col < LG_GRID; row++){

                grid [row][col] = userInput.at(col+row*LG_GRID);

        }

    }

}//Function





//outputs the small array

void outputSmallArray(char grid[SM_GRID]){



  for (int row=0;row <SM_GRID;row++){

    for(int col=0;col <SM_GRID;col++){

      cout << grid[row][col]<<" ";

    }

    cout << endl;

  }

}





//outputs the large array

void outputLgArray(char grid[LG_GRID]){



    for (int row=0;row <LG_GRID;row++){

    for(int col=0;col <LG_GRID;col++){

      cout << grid[row][col]<<" ";

    }

    cout << endl;

  }

}





//prompts for a command, and calls the appropriate function based on it

//returns true if command was valid

bool doCommand(char grid[LG_GRID]){



  bool valid = true;



  char input [MAXLEN];

  int command;



  cout << "Please enter 1 for FORWARDS or 2 for reverse!n";

  cin.getline(input,MAXLEN);



  command = atoi(input);

  switch (command){

  case FORWARD:

    cout << "Going Forwards !!!n";

    fillLgArray(grid,command);



    outputLgArray(grid);

    break;



  case REVERSE:

    cout << "Going backwards !!n";

    fillLgArray(grid, command);



    outputLgArray(grid);

    break;



  default:

    return false;

  }

 return valid;

}

In your fillLgArray function where you stated: You didn't know what to put for indexing into the user input string, there is a formula for indexing a 1D array to treat it as a 2D array. There are two variations for this formula one is for Row - Colum major and the other is for Col - Row major. In your particular situation if the user enters this from the console:

abcdabcdabcdabcd

You can count on the fact that std::string is very much like std::vector only that std::string stores its contents as char_type and has special member functions for working with string manipulation other than that std::string at the core is basically a specialized version of std::vector. Both of these containers from the stl are wrappers around a contiguous block of memory that it allocates into dynamic memory. These containers wrap around a type [size] array and they grow dynamically.

So knowing this we can treat the text from the console "abcdabcdabcdabcd" as an 1D array of characters like this:

 0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15

[a] [b] [c] [d] [a] [b] [c] [d] [a] [b] [c] [d] [a] [b] [c] [d]

So when you are traversing a double for loop to index into a 2D array you have to mentally step through the loop on each iteration.

In C languages such as C & C++ the indexing of a flat 1D array to represent a 2D array is Row-Major so the formula is as follows:

for ( row = 0; row < 4; row++ ) {

    for ( col = 0; col < 4; col ++ ) {

        2darray[row][col] = 1darray[(row * row_size or width) + col];

    }

}

This has already been asked and answered here! Map a 2D array onto a 1D

Here is a working example of your code in a minimal, complete verifiable example:

#include <string>

#include <iostream>

#include <exception>



#define LG_GRID = 4;



void fillArray( char grid[LG_GRID] ) {

    std::string userInput;

    std::cout << "Please enter 16 charactersn";

    std::cin >> userInput;



    if( userInput.length() < 16 )

        throw std::runtime_error( "Not enough characters" );

    if( userInput.length() > 16 )

        userInput = userInput.substr( 0, 16 );



    std::cout << "You entered " << userInput << 'n';



    for( int row = 0; row < LG_GRID; row++ ) {

        for( int col = 0; col < LG_GRID; col++ ) {

            // grid[row][col] = userInput[row * LG_GRID + col];

            grid[row][col] = userInput.at( row * LG_GRID + col );

            // both lines above will work however `string.at()` will throw an out of range exception.

        }

    }

}



void displayArray( char grid[LG_GRID] ) {

    for( int row = 0; row < LG_GRID; row++ ) {

        for( int col = 0; col < LG_GRID; col++ ) {

            std::cout << grid[row][col] << " ";

        }

        std::cout << 'n';

    }

}



int main() {

    try {

        char myGrid[LG_GRID][LG_GRID];

        fillArray( myGrid );

        displayArray( myGrid );    



    } catch( const std::runtime_error& e ) {

        std::cerr << e.what() << 'n';

        return EXIT_FAILURE;

    }



    return EXIT_SUCCESS;

}

And using the input you described: "abcdabcdabcdabcd" The output on the console to this program is:

Please enter 16 characters

abcdabcdabcdabcd

You entered abcdabcdabcabcd

a b c d

a b c d

a b c d

a b c d

Looking at your "IDK what to put here" line, you should probably use charAt. Something like:

grid [row][col] = userInput.at(col+row*4);

You want the character at user's input, spot 0, 1, 2, 3, 4, 5...etc

     String inputString = "abcdabcdabcdabcd";

     inputString = inputString.substring(0, 16);

     char inputChar = inputString.toCharArray();

     for (int i = 0; i < 4; i++) {

         String printRow = "";

        for (int j = 0; j < 4; j++) {

            printRow = printRow + inputChar[j];

        }

        System.out.println(printRow);

    }