Explain a section of code

[Shawn Blancett]

Can anyone explain the function bool check to me and how its working? Im just really confused trying to understand it in context with the program.

#include <iostream>
#include <cstdio>
#include <cstdlib>

using namespace std;

void display();
bool check(int a, int b);
int drop(int b, char player);

char place[6][7];  //available for whole program

int main()
{
    // put white spaces
    for(int a =0; a <= 5; a++){        
        for(int b = 0; b <= 6; b++)    
            place[a][b] = ' ';        
    }    
                                
    display();//Displays empty board
    int hold;//user row choice
    int hold2 = 0;//drop value
    int charsPlaced = 0;//Number of peices dropped so can end game if a draw
    bool gamewon = false;//Will be changed to true when game is won and will exit while loop
    char player = 'B';//start as player 2 will change back 2 player 1
    
    while(!gamewon){//will stop when game is won, ! means NOT makes the oppisite be checked
        if(hold2 != -1){//check if there was a error in the last drop
            if(player == 'B'){//if player 2 lasted dropped a piece so its player 1s turn
                cout<<"player 1 drop where?";
                player = 'A';//char of players piece
            }
            else{
                cout<<"player 2 drop where?";
                player = 'B';//char of player piece
            }
        }
        while(true){//will run untill 'break;'
            if(charsPlaced == 42) break;//if draw
            cin>>hold;//get user input
            hold--;//take off 1 to account for arrays starting at 0 not 1
            if(hold <=6 && hold>= 0) break;//if within valid range stop loop
            else cout<< "\nplease enter a value between 1 and 7 :";//ask for input and loop again
            if (cin.fail())    //catch a non number
            {                        //
                cin.clear();        //Stops cin trying to put its value in to hold
                char c;            //Try entering a non number without this, 2 see what this does
                cin>>c;            //
            }                        //Catch a non number

        }
        if(charsPlaced == 42) break;//if draw
        hold2 = drop(hold,player);//drop the player store the row in hold2
        if(hold2 == -1)    cout<<"Colom is full\nPlease enter anothor number between 1 and 7:";//if error -1 row is full
        else{
            gamewon = check(hold2,hold);//check if game is run
            charsPlaced ++;//another character has been succesfully placed
            system("cls");//This clears the screen works with windows, not nesscery to run game
            display();//displayed updated board
        }
    }
    
    system("cls");//this clears the screen
    
    if(charsPlaced == 42){//if draw
        cout<<"No winner, Game was draw\n";
        system("pause");
        return 0;
    }
    
    if(player == 15)//if won by player 2
        cout<<"gamewon by : player 2\n";
    else cout<<"gamewon by : player 1\n";//Else won by player 1
    
    system("pause");//pauses before exit so players can see who won, works with windows
    
    return 0;//Exit application
}

void display()
{
    cout<<" 1   2   3   4   5   6   7\n";
    for(int a = 0; a <= 5; a++)
    {
        for(int b =0; b <= 6; b++) cout<<"-"<<"-"<<"-"<<"-";
        cout<<'\n';
        for(int b =0; b <= 6; b++) cout<<"|"<<place[a][b]<<" "<<"|";
        cout<<'\n';
        for(int b =0; b <= 6; b++) cout<<"-"<<"-"<<"-"<<"-";
        cout<<'\n';
    }
}

bool check(int a, int b)
{
    int vertical = 1;//(|)
    int horizontal = 1;//(-)
    int diagonal1 = 1;//(\)
    int diagonal2 = 1;//(/)
    char player = place[a][b];
    int i;//vertical
    int ii;//horizontal
    
    //check for vertical(|)
    for(i = a +1;place[i][b] == player && i <= 5;i++,vertical++);//Check down
    for(i = a -1;place[i][b] == player && i >= 0;i--,vertical++);//Check up
    if(vertical >= 4)return true;
    
    //check for horizontal(-)
    for(ii = b -1;place[a][ii] == player && ii >= 0;ii--,horizontal++);//Check left
    for(ii = b +1;place[a][ii] == player && ii <= 6;ii++,horizontal++);//Check right
    if(horizontal >= 4) return true;
    
    //check for diagonal 1 (\)
    for(i = a -1, ii= b -1;place[i][ii] == player && i>=0 && ii >=0; diagonal1 ++, i --, ii --);//up and left
    for(i = a +1, ii = b+1;place[i][ii] == player && i<=5 && ii <=6;diagonal1 ++, i ++, ii ++);//down and right
    if(diagonal1 >= 4) return true;
    
    //check for diagonal 2(/)
    for(i = a -1, ii= b +1;place[i][ii] == player && i>=0 && ii <= 6; diagonal2 ++, i --, ii ++);//up and right
    for(i = a +1, ii= b -1;place[i][ii] == player && i<=5 && ii >=0; diagonal2 ++, i ++, ii --);//up and left
    if(diagonal2 >= 4) return true;
    
    return false;
}

int drop(int b, char player)
{
    if(b >=0 && b<= 6)
    {
        if(place[0][b] == ' '){
            int i;
            for(i = 0;place[i][b] == ' ';i++)
                if(i == 5){place[i][b] = player;
            return i;}
            i--;
            place[i][b] =player;
            return i;

        }
        else{
            return -1;
        }
    }
    else{
        return -1;
    }
}

[Salem]

> char place[6][7]; //available for whole program
It would be a lot better if you had some constants to define the size of the array.

const int ROWS = 6;
const int COLS = 7;
char place[ROWS][COLS]; //available for whole program

It would also be a good idea if you localised this array in main, and passed a parameter to all the functions which need access to it.
Making things global is a lazy habit.

If you want to understand check, then rewrite all of the compressed loops into long form
> for(i = a +1;place[i][b] == player && i <= 5;i++,vertical++);//Check down
As

    for(i = a +1;i <= 5;i++) {
        if ( place[i][b] == player ) {
            vertical++;
        }
    }

1. It is clearer.
2. It removes an overflow bug in the original code, caused by testing the array before testing the subscript.

You might then try say this, to observe how it runs.

    for(i = a +1;i <= 5;i++) {
        if ( place[i][b] == player ) {
            vertical++;
            cout << "DEBUG: Incrementing vertical at subscript i=" << i << endl;
        }
    }

I guess that's what happens when you randomly grab 'found' code from the web. Cite your references when you copy/paste.

Here's one, ConnectFour/connect4.cpp at master * thatSunshineKid/ConnectFour * GitHub
There are others.
GIYF