Entering numbers at the Serial Monitor

hello all,
i'm using uno + xbee series 1 + lcd mirror reading @ gas meter - difficulty in reading thing sited. real novice here, have managed going point hall sensor @ meter picks each dial rotation , adds lcd display in house. real readings displayed, need input 9 digit number "offset" incoming pulses added.

i playing around published sketches (thank you) code below.

code: [select]

int incomingbyte = 0;   // incoming serial data
string instring = "";    // string hold input

void setup() {
  // put setup code here, run once:
serial.begin(9600);     // opens serial port, sets data rate 9600 bps
  serial.print ("enter data @ command line , check set newline");
  serial.print("\n");//needs display "value" , "string" - if omitted, displays "string" first time round
}

void loop() {
            // put main code here, run repeatedly:
             // send data when receive data:
            if (serial.available() > 0) {
                // read incoming byte:
                incomingbyte = serial.read();
                 if (isdigit(incomingbyte)) {
      // convert incoming byte char
      // , add string:
      instring += (char)incomingbyte;
    }
                 if (incomingbyte == '\n') {
      serial.print("value:");
      serial.println(instring.toint()*2);
      serial.print("string: ");
      serial.println(instring);
      // clear string new input:
      instring = "";
    }

             
        }
}

i have changed of text messages , added 1 calculation (*2).

if enter 999999999 (i.e.9 digits), ok - if tenth digit added, overflows.

can tell me why happens, , significance of "overflow" number comes on serial monitor?

thanks

quote

int incomingbyte = 0;   // incoming serial data

why? if name implies byte, why type not byte? use name implies.

code: [select]

                 if (isdigit(incomingbyte)) {
isdigit() expects char.

code: [select]

      // convert incoming byte char
      // , add string:
      instring += (char)incomingbyte;
another clue correct type variable.

quote

if enter 999999999 (i.e.9 digits), ok - if tenth digit added, overflows.

have looked @ documentation toint() method? despite stupid name, not return int. 10 character value trying enter fit in variable of type toint() returns?

there reason reference page. expected use it.

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