I want to easily send a number from a phone to my esp8266. I have an app that sends the number in the format IP/number. How can I modify the code to give my the number behind the IP address as an integer?

#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>

MDNSResponder mdns;

// Replace with your network credentials
const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";

ESP8266WebServer server(80);

String webPage = "";

void setup(void){

  WiFi.begin(ssid, password);

  // Wait for connection
  while (WiFi.status() != WL_CONNECTED) {
  Serial.print("Connected to ");
  Serial.print("IP address: ");

  if (mdns.begin("esp8266", WiFi.localIP())) {
    Serial.println("MDNS responder started");

  server.on("/", [](){
    Serial.println("device connected");
  Serial.println("HTTP server started");

void loop(void){

So it would do something like this for and should be looking through every i between 0 and 200. :

server.on("/"+String(i), [](){

2 Answers 2


First of all use the event function server.on with a path that corresponds to your function and use a url like this:

With a url parmeter for your number. Your code might look like this:

At the top:

int nums_size = 0;
const int nums_max = 128;
int nums[nums_max];

In setup:

server.on("/recordnumber", [](){
    int num;
    if(server.hasArg("num")) {
      String num_str = server.arg("num");
      if(num_str.charAt(0) == '0') {
        num = 0;
      } else {
        num = num_str.toInt();
        if(num == 0) {
          server.send(400, "text/plain", "not a number");
      if(nums_size < nums_max) {
        nums[nums_size++] = num;
        server.send(200, "text/plain", "saved");
      } else {
        server.send(500, "text/plain", "full");
    } else {
      server.send(400, "text/plain", "bad params");

First you need to extract the string that contains the number (after the /). Since it is already stored in consecutive memory you can pass the pointer to the character after the / symbol to the C function atoi to convert it to an integer.

I assume the pointer is already \0 terminated.

You can use the C function strchr to search for the / symbol.

Tip: use a C compiler on a desktop/PC to check how these functions work. Once you know how to use them, copy them in your Arduino code. This is much faster than uploading/debugging sketches probably.

  • My phone accesses the ESP via it's IP address for instance: or The ESP should than store these values 100 and 200 into integers but these numbers could be any number
    – luukito
    Commented Jan 3, 2018 at 13:06
  • I adapted the answer, use strchr to search for the / symbol, than use atoi Commented Jan 3, 2018 at 13:09
  • But in order to extract the right part of the string how do you store the whole incoming IP address in a string?
    – luukito
    Commented Jan 3, 2018 at 13:12
  • WiFi.localIP() is already pointing to a string, you can use this as input for strchr to search for the / symbol, than you can use atoi. Commented Jan 3, 2018 at 14:09

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