[RyDeR`]

Use replaceChar since they're both just characters from the ASCII table:

pawn Код:

stock replaceChar(strSrc[], chWhat, chWith)
{
    for(new i; strSrc[i] != EOS; ++i)
    {
        if(strSrc[i] == chWhat)
        {
            strSrc[i] = chWith;
        }
    }
}

pawn Код:

replaceChar(string, '\n', '~');

EDIT: Works fine for me with very long strings