C: Function 当矩阵维度为奇数时，以矩阵为参数打印错误

Question

so I created a function that has a matrix as an argument. The matrix is made out of 0's and 1's. The objective of this function to read the matrix values, one by one and in case they are a 0 it prints out a "~", in case they are a 1 it prints "B" and in case they are a 0 next to a 1 horizontaly it prints a "]".

Here's the function:

void canvas(int m[t1][t2]){

    for (int i = t1 - 1; i > -1; i--)
    {
        for (int j = 0; j < t2; j++)
        {
            if (m[i][j] == 1){
                printf("B ");
            }
            else if (m[i][j] == 0 && (m[i][j + 1] == 1 || m[i][j - 1] == 1)){
                printf("] ");
            }
            else {
                printf("~ ");
            }
        }
        printf("\n");
    }
}

This is what the matrix used as an argument looks like (example of 13 x 13):

0 0 0 0 0 0 0 0 0 0 0 0 0 
0 1 1 1 1 1 1 1 1 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 0 0 0 0 0 0 0 1 0 0 0 
0 1 1 1 1 1 1 1 1 1 0 0 0 
0 0 0 0 0 0 0 0 0 0 0 0 0 

This is the output I expected:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 
] B B B B B B B B B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B B B B B B B B B ] ~ ~ 
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 

And this is what I'm getting:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ] 
] B B B B B B B B B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B ] ~ ~ ~ ~ ~ ] B ] ~ ~ 
] B B B B B B B B B ] ~ ~ 
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 

That last character on the first line always appears wrong when both dimensions of the matrix are odd numbers and I can't figure out why. I think it might have to do with the logical expression but can't find a reason for this to be happening with the odd numbers.

Answer 1

When you do this check:

else if (m[i][j] == 0 && (m[i][j + 1] == 1 || m[i][j - 1] == 1)){

You read off the end of the array when j is either 0 or t2-1 . Doing so triggers undefined behavior

You need to do an additional check for these cases:

else if (m[i][j] == 0 && ((j < t2-1 && m[i][j + 1] == 1 ) || 
                          (j > 0) && m[i][j - 1] == 1)) {