Method verification problem

I made this function for the old game:

void jogadaPC(char m[][3], char opc)
{

    puts("\nVez do computador.");
    sleep(1); 

    int linha = rand() % 2;
    int coluna = rand() % 2;

    bool vazio = localVazio(m, linha, coluna);
    bool valido = false;

    if(!vazio)
    {
        while(!valido)
        {
            linha = rand() % 2;
            coluna = rand() % 2;
            if(localVazio(m, linha, coluna))
            {
                m[linha][coluna] = opc;
                valido = true;
            }
        }
        return;
    }
    m[linha][coluna] = opc;
}

In that it chooses a position (row, column) randomly in the array, and if it is false it passes the while check, but it never ends.

So: I started all array values with '':

void iniciar(char m[][3])
{

    for(int i=0; i<3; i++)
    {
        for(int j=0; j<3; j++)
        {
            m[i][j] = ' ';
        }
    }
}

But he is not going through this method here:

bool localVazio(int m[][3], int lin, int col)
{
    return m[lin][col] == ' ';
}

Which by default would return true to empty.