function int StrToInt(str s)
{
    int integer = 0;
    bool negative = GetChar(s, 0)=='-';
    int j;
    int i = 0;
    if (GetChar(s, 0) == '-' || GetChar(s, 0) == '+')
        i++;

    for(; i < StrLen(s); i++)
    {
        int c = GetChar(s, i);
        if (c < '0' || c > '9') return 0; // invalid int
        c -= '0';
        int multiplier = StrLen(s)-i;
        for (j = 1; j < multiplier; j++)
            c *= 10;
        integer += c;
    }

    if (negative) integer = -integer;
    return integer;
}