What is the ERROR in this program?

Projects Programming
1

hi!

#include <SoftwareSerial.h>
SoftwareSerial SIM900(6, 7);
  void donothing();

char incoming_char=0;
 
void setup()
{
  Serial.begin(19200); // for serial monitor
  SIM900.begin(19200); // for GSM shield
  //SIM900power();  // turn on shield
  delay(20000);  // give time to log on to network.
 pinMode(2, OUTPUT);
 
 pinMode(4, INPUT);
 
}
 

 
void loop()
{
  // reading any text is available
  if(SIM900.available() >0)
  {
    
    delay(3000);
  while (digitalRead (4 == LOW)){
    void donothing();
 
  }
  }
  else if (digitalRead (4 == HIGH))
  {
    digitalWrite (2, HIGH);
   delay (3000);
  digitalWrite (2, LOW); 
delay (3000);
 SIM900.println("AT+CMGD=1,4"); // delete all SMS//Serial.print(incoming_char); 

  }

}


 void donothing()
 
 {
   
 }

This is my new program, if any text message available it have to go for-> do nothing() loop, While digital read 4 th pin LOW, after that if next time received sms then only it has to go for do nothing loop().

without sms if I press the pin 4 is HIGH it has to blink the led pin 2 one time.

but my errors are

if it receive the sms after do nothing loop is executing but it is not retrieving after I low the pin 4 ,

and also if I didn't sent the sms it is directly make a HIGH on digital pin 2. without press the 4th pin it is continuously blinking lED. but if I press the 4th pin then only it have to blink the led pin 2 if I release 4 th pin it it should not do anything while next time button 4 press or receive sms.

please help me thank you.

2 
  while (digitalRead (4 == LOW)){
    void donothing();

There are multiple things wrong with that.

Instead of:

while (digitalRead (4 == LOW))

You want:

while (digitalRead (4) == LOW)

You don't need to make a function that does nothing. Just do:

while (digitalRead (4) == LOW)
  { }  // do nothing
3

Now repeatedly do nothing is executing,

4

Now repeatedly do nothing is executing,

As long as digitalRead (4) == LOW is true
"Now repeatedly do nothing is executing" will always happen

5 
#include <SoftwareSerial.h>
SoftwareSerial SIM900(6, 7);
  void donothing();

char incoming_char=0;
 
void setup()
{
  Serial.begin(19200); // for serial monitor
  SIM900.begin(19200); // for GSM shield
  //SIM900power();  // turn on shield
  delay(20000);  // give time to log on to network.
  
  
   SIM900.print("AT+CMGF=1\r");  // set SMS mode to text
  delay(100);
 pinMode(2, OUTPUT);
 
 pinMode(4, INPUT);
 
}
 

 
void loop()
{
  // reading any text is available
  if(SIM900.available() >0)
  {
    delay(3000);
      while (digitalRead (4)== LOW)
      Serial.print("hi");
 { }
  
  } 
  
  delay(3000);
 if (digitalRead(4) == HIGH)
  {
    digitalWrite (2, HIGH);
   delay (3000);
  digitalWrite (2, LOW); 
delay (3000);
 SIM900.println("AT+CMGD=1,4"); // delete all SMS//Serial.print(incoming_char); 

  }

}


 void donothing()
 
 {
   
 }

yeah! but once I send the message it is entering the do nothing loop after I press it it is jumped to next part if release this again it is executing do nothing part, but exactly I need only one time do nothing have to work while I press 4 after that if I send the next time then only it have to work.

6

Venki:
yeah! but once I send the message it is entering the do nothing loop after I press it it is jumped to next part if release this again it is executing do nothing part, but exactly I need only one time do nothing have to work while I press 4 after that if I send the next time then only it have to work.

I see ...

7

anybody pls tell me what is error here

8 
anybody pls tell me what is error here

Your indenting is piss-poor. There is no excuse for that, given that there is an Auto Format item on the tools menu.

You have useless curly braces.

You have useless functions.

You have not been anywhere near clear on what the code is doing, what you want it to do, or how those two differ.

So, how can we possibly help you?