Problem changing characters of an array

Question

I have a problem where given a 10x10 matrix, it has to be filled with asterisk characters and the’t'. In this matrix, ONLY the characters with the coordinates that have t' and that are neighboring the coordinates with characters containing asterisk have to be replaced by the character 'p', as shown below:

The code I developed can do the substitution, but it has a problem: it converts all’t' that are located at the left and right end of the matrix. Follow the code below:

using namespace std;

int main() 
{
  char matriz[10][10];

  for(int i=0; i<10; i++)
  {
    for(int j=0; j<10; j++)
    {
      cin >> matriz[i][j];
    }
  }

  for(int i=0; i<10; i++)
  {
    for(int j=0; j<10; j++)
    {
      if(matriz[i][j] == 't')
      {
        if( 
           matriz[i-1][j] == '*' || 
           matriz[i+1][j] == '*' || 
           matriz[i][j-1] == '*' || 
           matriz[i][j+1] == '*')
          {
            matriz[i][j] = 'p';
          }
      }
    }
  }

  cout << endl;

  for(int i=0; i<10; i++)
  {
    for(int j=0; j<10; j++)
    {
      cout << matriz[i][j]<< " ";
    }
    cout << endl;
  }
}

I set up a matrix that shows the problem:

ENTRADA:
* * * t t t * * * *
* * t t t t * * * *
* t t t t t t * * *
* * * * t t t t t t
* * * * * t t t t t
* * * * * t t t * t
* * * * t t t t * *
t t t t t t t t t *
t t t t t t t t * *
t t t t t * * * * *

SAÍDA:
* * * p t p * * * * 
* * p t t p * * * * 
* p p p t t p * * * 
* * * * p t t p p p 
* * * * * p t t p p 
* * * * * p t p * p 
* * * * p t t p * * 
p p p p t t t t p * 
p t t t t p p p * * 
p t t t p * * * * * 

As you can see, the’t' in the 4x9 and 8x0 coordinates also changes, which is wrong.

Answer 1

You have a burst of indices at the narrowness of your matrix. On the line [8,0], the condition matriz[i][j-1] looking for a position that does not exist in the case j-1, where j = -1, this occurs in all rows of column 0. Also occurs this burst at the right end in column 9, where the calculation j + 1, results in j = 10 and this Dice does not exist in the matrix.

For the lines also occurs the same at the ends. To solve do a check for each end.

#include <iostream>
using namespace std;

int main() 
{
  char matriz[10][10] ={{'*','*','*','t','t','t','*','*','*','*'},
                        {'*','*','t','t','t','t','*','*','*','*'},
                        {'*','t','t','t','t','t','t','*','*','*'},
                        {'*','*','*','*','t','t','t','t','t','t'},
                        {'*','*','*','*','*','t','t','t','t','t'},
                        {'*','*','*','*','*','t','t','t','*','t'},
                        {'*','*','*','*','t','t','t','t','*','*'},
                        {'t','t','t','t','t','t','t','t','t','*'},
                        {'t','t','t','t','t','t','t','t','*','*'},
                        {'t','t','t','t','t','*','*','*','*','*'}};

  for(int i=0; i<10; i++)
  {
    for(int j=0; j<10; j++)
    {
      cout << matriz[i][j]<< " ";
    }
    cout << endl;
  }

  cout << endl;
  cout << endl;
  for(int i=0; i<10; i++)
  {
    for(int j=0; j<10; j++)
    {

      if( (matriz[i][j] == 't') && (matriz[i+1][j] == '*') && (i + 1) < 10 )
      {
        matriz[i][j] = 'p';
      }

      else if( (matriz[i][j] == 't') && (matriz[i-1][j] == '*') && (i -  1) >= 0 )
      {
        matriz[i][j] = 'p';
      }

      else if((matriz[i][j] == 't') && ((j +  1) < 10) && matriz[i][j + 1] == '*')
      {
        matriz[i][j] = 'p';
      }

      else if((matriz[i][j] == 't') && ((j -  1) >= 0) && matriz[i][j - 1] == '*')
      {
        matriz[i][j] = 'p';
      }    
    }  
  }


  for(int i=0; i<10; i++)
  {
    for(int j=0; j<10; j++)
    {
      cout << matriz[i][j]<< " ";
    }
    cout << endl;
  }
}