issues with a script

im getting sytax errors at this one point and cant seam to figure it out help will be greatfull

key lastSensed;
string display;
string lastSpeed;
string n1 = "";
string n2 = "";
string gsHexChars = "0123456789ABCDEF";
string Int2Hex(integer iInt)
{
    integer iWork = iInt & 0xF;
    string sResult = llGetSubString(gsHexChars, iWork, iWork);
    iInt = (iInt >> 4) & 0x0FFFFFFF;

    while (iInt != 0)
    {
        iWork = iInt & 0xF;
        sResult = llGetSubString(gsHexChars, iWork, iWork) + sResult;
        iInt = iInt >> 4;
    }

    return(sResult);
} // string Int2Hex


string Round2String(float fValue, integer iDecimals)
{
    integer iValue = (integer)fValue;
    integer iRemainder = llRound((fValue - iValue) * llPow(10, iDecimals));

    if (!iRemainder)
    {
        return (string)iValue + ".00";
    }
    else
    {
        return (string)iValue + "." +(string)llAbs(iRemainder);
    }

} // Round2String


string Vector2String(vector vVector, integer iDecimals)
{
    return("<" + Round2String(vVector.x, iDecimals) + ", " +
        Round2String(vVector.y, iDecimals)+ ", " +
        Round2String(vVector.z, iDecimals) + ">");
} // Vector2String


default 
{
    on_rez(integer start_param) 
    {
        llResetScript();
    }
    
    state_entry() 
    {
        llSensorRepeat("", "", AGENT, 10.0, PI/4, 1);
    }
    sensor(integer num_detected) 
    {
        string speed = Round2String(llVecMag(llDetectedVel(0)), 2);
        integer decimalIndex = llSubStringIndex(speed, "");
        speed = llGetSubString(speed, 0, decimalIndex );
        integer newSpeed = (lastSpeed != speed);
        if(speed > 10) // ERROR!
        {
            llWhisper(0,"0"+speed);
        }
        else if(speed < 10) // ERROR!
        {
        llSetText(llDetectedName(0) + " is moving at " + speed + "m/s.",<1,1,1>,1);
        lastSpeed = speed;
        }
    }
    no_sensor()
    {
        llSetText("",<1,1,1>,1);
    }
}

You're getting syntax errors because "speed" is a string, but you're trying to use it like a number. The quickest solution is probably to declare it as a float, and then cast the result of the relevant functions to match, e.g. like this:

float speed = (float)Round2String(llVecMag(llDetectedVel(0)), 2);

Of course, then you'll need to cast the speed to a string when you want to output it in llWhisper or whatever.