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So I am running my project on a NodeMCU, but I don't know how to let it add a yield in front of an else if. It will give me an error like this:

Arduino:1.8.12 (Windows 10), 開發板:"NodeMCU 1.0 (ESP-12E Module), 80 MHz, Flash, Legacy (new can return nullptr), All SSL ciphers (most compatible), 4MB (FS:2MB OTA:~1019KB), 2, v2 Lower Memory, Disabled, None, Sketch + WiFi Settings, 115200"

G:\資優班\科展\程式碼\Front_End\Main_Code_V5\Main_Server\Main_Server.ino: In function 'void loop()':

Main_Server:84:5: error: 'else' without a previous 'if'

exit status 1 'else' without a previous 'if'

This report would have more information with "Show verbose output during compilation" option enabled in File -> Preferences.

Here's the code:

#include <SPI.h>
#include <ESP8266WiFi.h>

#define MAX_SRV_CLIENTS 2
#define led LED_BUILTIN

WiFiServer server(80);
WiFiClient serverClients[MAX_SRV_CLIENTS];
IPAddress ip(10, 241, 241, 27);
IPAddress mask(255, 255, 255, 0);
IPAddress gateway(10, 241, 241, 254);
char ssid[] = "AP";
char pass[] = "Science_Fair";

void setup() {
  Serial.begin(9600);
  WiFi.config(ip, gateway, mask);
  WiFi.begin(ssid, pass);
  while (WiFi.status() != WL_CONNECTED) {
    yield();
  }
  server.begin();
  pinMode(led, OUTPUT);
  digitalWrite(led, LOW);
}

void loop() {
  uint8_t i;
  Serial.setTimeout(10);
  for (i = 0; i < MAX_SRV_CLIENTS; i++) {
    Serial.println("Pre 1");
    if (server.hasClient()) {
      Serial.println("Pre 2");
      if (!serverClients[i] || !serverClients[i].connected()) {
        Serial.println("Pre 3");
        if (serverClients[i]) {
          Serial.println("Pre 4");
          serverClients[i].stop();
          Serial.println("Pre 5");
        }
        Serial.println("Pre 6");
        serverClients[i] = server.available();
        Serial.println("Pre 7");
        serverClients[i].setTimeout(10);
        Serial.println("Pre 8");
        Serial.print("New client: ");
        Serial.println("Pre 9");
        Serial.println(i);
        Serial.println("Pre 10");
        break;
      }
    }
    yield();
  }
  for (i = 0; i < MAX_SRV_CLIENTS; i++) {
    String fromClient = serverClients[i].readStringUntil('e');
    Serial.println("P1");
    yield();
    if (fromClient == "LR") {
      Serial.println("LR");
      String reply = Serial.readStringUntil('e');
      Serial.println("P2");
      yield();
      if (reply == "Warn_B") {
        yield();
        Serial.println("Confirm");
        Serial.println("P3");
        for (i = 0; i < MAX_SRV_CLIENTS; i++) {
          serverClients[i].print("Warn_B");
          Serial.println("P4");
          yield();
        }
      }
    }
    yield(); // this is the yield I need to add
    else if (fromClient == "RR") {
      Serial.println("RR");
      Serial.println("P5");
      String reply = Serial.readStringUntil('e');
      Serial.println("P6");
      yield();
      if (reply == "Warn_A") {
        Serial.println("P7");
        Serial.println("Confirm");
      }
      for (i = 0; i < MAX_SRV_CLIENTS; i++) {
        serverClients[i].print("Warn_A");
        Serial.println("P8");
        yield();
      }
    }
    yield();
  }
}

I need the yield() there but I don't know how to let it still do the else if. Please help me guys, thanks!

  • 3
    Why do you think you need a yield there? – Majenko Apr 6 '20 at 10:03
  • @Majenko Uh cuz I am using my NodeMCU and I have a watchdog timer, I think there is the problem cuz it is always giving me a bunch of errors like feefeffe – Sax Ted Apr 6 '20 at 10:08
  • 1
    Yes, but why there? Why between two pieces of code that are "either / or"? If the first ran then the second won't. If the second ran then the first won't have. There's no "between" in that scenario. – Majenko Apr 6 '20 at 10:11
  • the yield() before the if is the yield() before the else – Juraj Apr 6 '20 at 13:23
1

First of all do yourself a favour and listen to your IDE

This report would have more information with
 "Show verbose output during compilation"
option enabled in File -> Preferences.

and in an if else there is no in between so either let it run as a state machine especially inyour case A != B != C != other:

void subfunction(){
  if(A){
  // code to run
  return; 
  }
 yield();  
 if(B){
  // code to run
  return; 
  }
 yield();
 if(C){
  // code to run
  return; 
  }
 else{}  // to catch if not A or B or C
 yield();
}

or implement switch case (Pseudo code)

 switch(fromClient){
    case "LR":
      //code to run
      yield();
      break;
    case "RR":
      //code to run
      yield();
      break;
    default:
      //code to run
      yield();
      break;
  }

Id else chains are prone to errors as in your case its A != B != C != other

  • Thank you! But again I am at home, I'll test it tmr in my lab, thank you again! – Sax Ted Apr 6 '20 at 11:23
  • why not yield() after the switch? – Juraj Apr 6 '20 at 13:20
  • I just copied his"use case" but you are right he could even do it before the cases and in the case (depends on his WD timer – Codebreaker007 Apr 6 '20 at 13:38

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