Method required In C which is Equivalent to DoEvents method in VB 6.0 to access GSM Modem

I need to write a code in C to access GSM Modem thro' serial port. I already done successfully. But I need help to write a method in C which is equivalent to DoEvents in VB 6.0. That is, I declared global variable OK in C. If I try to retrieve the value in the middle of the process I could not able to get the correct value though the I set the OK value equal to true in the middle of the process. This can be acheieved using DoEvents method in VB 6.0 and already did this and got the result correctly. But not in C. I am new to C. Please go thro' my code and help me.

I opened the Serial port in Non-Overlapped mode.

Code:

#include <string>
#include <windows.h>
#include <time.h>

using namespace std;

//STRUCTURE TO STORE TELEPHONE BOOK (THE COM OUTPUT)

typedef struct{
	char splitRecs[25];
} phBook;
phBook record[50];

char INBUFFER[500];
char OUTBUFFER[500];
char * chrArray;
static string strArray;
bool greaterSign = false;

//SMS VARIABLES
bool Message_Store = false;
string Message_Buffer;
char *SMS_MesgNum = NULL;
char *SMS_TelephoneNum = NULL;

// PORTS
HANDLE h_GSM = NULL;
DCB dcbConfig;
COMMTIMEOUTS CommTimeouts;
	
DWORD dwEventMask;
DWORD bytes_read    = 0;    // Number of bytes read from port
DWORD bytes_written = 0;

//VARIABLES USED IN FUNCTION ComEvent
bool OK = false;
bool Error = false;
bool RING = false;

// FUNCTIONS USED IN THIS PROGRAM
int WriteCOM();
int ReadCOM();
static void doEvents();
void wait_for_response();
char *substring(size_t start, size_t stop, char src[]);
int split(char input[], const char *delims);
void ComEvent(char Event[]);
void wait_for_response();
static void doEvents();

// WRITE TO THE PORT
int WriteCOM(){
	 
     if(!WriteFile(h_GSM,           // Handle
		   &OUTBUFFER,      // Outgoing data
		   20,              // Number of bytes to write
		   &bytes_written,  // Number of bytes written
		   NULL)){          
		// error processing code here
		printf("Error in writing\n");
		return 0;
	}
 return 0;
}

// READ THE PORT
int ReadCOM(){
	strcpy(&INBUFFER[0], "");
	memset(INBUFFER, 0, sizeof(INBUFFER));
			
	do
	{				
	    if(ReadFile(h_GSM, &INBUFFER, sizeof(INBUFFER),   
               &bytes_read, NULL) != 0){
				   
	    }
			
	}while(bytes_read > 0);
			
	//printf("%d\n", bytes_read);
return 0;
}

// FUNCTION TO EXTRACT SPECIFIED NUMBER OF SUBSTRING FROM THE OUTPUT
char *substring(size_t start, size_t stop, char src[])
{
   
   size_t size = sizeof(src);
   
   char* dst = (char*) malloc(strlen(src) * sizeof(char));
   int count = stop - start;
   
   sprintf(dst, "%.*s", count, src + start);
   return dst;
}

//SPLIT COM OUTPUT AND STORE THE PHONE BOOK INTO ARRAY
int split(char input[], const char *delims){	
	char *output[500];
	int loop;
	double NumOfStr_Input = strlen(input);
	int i = 0;
    
	output[0] = strtok(input, delims); 
	
	if(output[0]==NULL) 
	{ 
		printf("No text to search.\n"); 
		exit(0); 
	} 
	
	for(loop=1;loop<numofstr_input;loop++)>
	{ 
	
		output[loop]=strtok(NULL,delims); 
		if(output[loop]==NULL) 
		break; 
	} 
	for(loop=0;loop<numofstr_input;loop++)>
	{ 
		if(output[loop]==NULL) 
		break; 
		//printf("Item #%d is %s.\n",loop,output[loop]); 
	
		//split(output[loop], delim);
		strcpy(record[i].splitRecs, output[loop]);
		i++;
		
	} 
	/*
	int j=0;
	
	for(;j < i;j++){
	
		printf("%s\n", record[j].splitRecs);
		
	}*/
return 0; 
}

// VALIDATE THE (GSM) COM OUTPUT
void ComEvent(char Event[]){
	
	// IF 'OK' RECEIVED FROM PORT, THE WRITE/READ COMMAND (IF ISSUED) SUCCEEDS
	if (strcmp(Event, "OK") == 0){
		
		OK = true;
		
	}
	// IF 'ERROR' RECEIVED FROM PORT, THE WRITE/READ COMMAND (IF ISSUED) FAILED
	
	if(strcmp(Event, "Error") == 0){
		
		Error = true;
		
	}
	
	// THIS IS USED TO FIND THE INCOMING CALLER ID TO VALIDATE. 
	// FOR EXAMPLE, IF SOMEONE CALLS THE GSM WE CAN EXTRACT THE CALLER MOBILE NUMBER
	// TO CHECK WHETHER HE/SHE IS ADMIN/OWNER OR ANONYMOUS, ETC USING 'CLCC' COMMAND
	
	if(strcmp(Event, "RING") == 0){
		
		RING = true;
		strcpy(&OUTBUFFER[0], "AT+CLCC\r");
		WriteCOM();
		
	}
	
	//CALL SUBSTRING FUNCTION TO IDENTIFY THE EVENT WHETHER IF IT IS SMS OR ELSE 
	substring(0, 5, Event); 
	
	// IF PHONE BOOK READ COMMAND ISSUED
	if(strcmpi(substring(0, 5, Event), "+CPBR") == 0){
		
		split(Event, ",");
		
	}
	
	// IF SMS Message received
	if(strcmpi(substring(0, 5, Event), "+CMTI") == 0){
		
		//Event = "";
		OK = false;
		Error = false;
		
		split(Event, ",");
		//Event = "";
		int lenSMS_MesgNum = strlen(record[1].splitRecs);
		
		SMS_MesgNum = (char*) malloc(lenSMS_MesgNum * sizeof(int));
		sprintf(SMS_MesgNum,"%s",record[1].splitRecs);
		//Event = "";
		//getMessage(SMS_MesgNum, Event);
		
		// GETTING SMS
		char *MesgCmd = NULL;
		char ATCommand[] = "AT+CMGR=";
		char *Param = SMS_MesgNum;
		char term_char[] = "\r";
		MesgCmd = (char*) malloc((strlen(ATCommand) * sizeof(char)) + (strlen(Param) * sizeof(int)) + (strlen(term_char) * sizeof(char)) );
		
		sprintf(MesgCmd, "%s%s%s",ATCommand,Param,term_char );
		//printf("%s\n", MesgCmd);
        //return;
		strcpy(&OUTBUFFER[0], MesgCmd);
		WriteCOM(); //WRITING TO THE PORT
		//while (!OK){
			wait_for_response();
		//}
		
		//printf("%d\n", OK);
		if (OK == true){
			split(Event, ",");
			printf("%s\n", substring(1, 12, record[1].splitRecs));
			SMS_TelephoneNum = substring(1, 12, record[1].splitRecs);
			printf("%s\n", SMS_TelephoneNum);
		}
		
		
		//printf("%s\n", SMS_MesgNum);
		
		/*
		return;
		// JUST RETURN THE SMS NUMBER 1 FOR TESTING PURPOSE ONLY
		strcpy(&OUTBUFFER[0], "AT+CMGR=1\r");
		WriteCOM(); //WRITING TO THE PORT
		wait_for_response();
		*/
	}
	
	//IF GSM IS RECEIVING CALL
	if(strcmpi(substring(0, 5, Event), "+CLCC") == 0){
		
		split(Event, ",");
		//printf("%s\n", substring(4, 14, record[5].splitRecs));
		Event="";
		OK = false;
		Error = false;
		
		if (strcmpi(substring(4, 14, record[5].splitRecs), "9944232334")  == 0){
			printf("%s\n", "GSM Admin Calling...");
			
			/*
			strcpy(&OUTBUFFER[0], "ATH\r");
			WriteCOM();
			wait_for_response();
			
			char ATCommand[] = "ATD";
			char *mobileNum = substring(1, 14, record[5].splitRecs);
			char term_char[] = ";\r";
			char *NumToCall = NULL;
			NumToCall = (char*) malloc((strlen(ATCommand) * sizeof(char)) + (strlen(mobileNum) * sizeof(int)) + (strlen(term_char) * sizeof(char)));
			sprintf(NumToCall,"%s%s%s",ATCommand,mobileNum,term_char);
			strcpy(&OUTBUFFER[0], NumToCall);
			WriteCOM();
			*/
			
			//wait_for_response();
			//strcpy(&OUTBUFFER[0], "AT+CMGS=\x22substring(4, 14, record[5].splitRecs)\x22");
			
			
			//wait_for_response();
			//printf("%d\n", greaterSign);
			/*
			if (greaterSign == true){
				strcpy(&OUTBUFFER[0], "Confirmation SMS sent from GSM Unit\x1A");
				WriteCOM(); 
				wait_for_response();
			}*/
		}
		else{
			printf("%s\n", "Anonymous Call...");
			strcpy(&OUTBUFFER[0], "ATH\r");
			WriteCOM();
			wait_for_response();
		}
	}
  }
void wait_for_response(){
	   
   		  time_t seconds;
		  seconds = time (NULL);
		  
		  while (1)
		  {
			  
			  doEvents(); 
				
			  if(time(NULL) - seconds >= 5){
				break;
			  }
		  }
}
static void doEvents(){
		
	    MSG msg;
	    HWND hWnd;
		while( PeekMessage( &msg, hWnd, 0, 0, PM_REMOVE )){
						  
		   TranslateMessage( &msg );
		   DispatchMessage( &msg );
					   
		}	
}
//**********************************************************************
int main(int argc, char* argv[]){
	
	h_GSM = CreateFile(TEXT("COM1"),// open com1:
		GENERIC_READ | GENERIC_WRITE, // for reading and writing
		0,                            // exclusive access
		NULL,                         // no security attributes
		OPEN_EXISTING,                // Existing Port
		FILE_ATTRIBUTE_NORMAL,        // Non-overlapped ***
						NULL);
		if (h_GSM == INVALID_HANDLE_VALUE){
        // error processing code
		printf("Error Opening Port\n");
		return 0;
    }
    
    // Set timeouts in milliseconds
    CommTimeouts.ReadIntervalTimeout         = 0; 
    CommTimeouts.ReadTotalTimeoutMultiplier  = 0; 
    CommTimeouts.ReadTotalTimeoutConstant    = 100;
    CommTimeouts.WriteTotalTimeoutMultiplier = 0;
    CommTimeouts.WriteTotalTimeoutConstant   = 100;
    
	if(!SetCommTimeouts(h_GSM ,&CommTimeouts)){
	    // error processing code
		printf("Error setting timeouts");
		return 0;
	}
    
    // Set Port parameters.
    
    if(!GetCommState(h_GSM, &dcbConfig)){
		printf("Error getting Comm Settings");
		return 0;
	}
    
	dcbConfig.BaudRate = 9600;
        dcbConfig.StopBits = ONESTOPBIT;
        dcbConfig.ByteSize = 8;
        dcbConfig.Parity   = NOPARITY;
     
	if(!SetCommState(h_GSM, &dcbConfig)){
		printf("Error getting Comm Settings");
		return 0;
	}
	
	// DISABLE GSM MODEM 'ECHO' THE INPUT (TYPING)
	strcpy(&OUTBUFFER[0], "ATE0\r");
	WriteCOM();
	wait_for_response();

PROBLEM HERE!!!
	
******** HERE I HAVE TO CHECK THE STATUS OF "OK". IF IT IS '1' THEN START TO EXECUTE THE NEXT LINE. BUT I COULD NOT ABLE TO RECEIVE THE CORRECT STATUS OF THE "OK'. I ALWAYS RECEIVE FALSE.**********

        IF(OK == true){
	    // SET THE SMS IN TEXT MODE (PDU MODE IS DEFAULT = 0)
	       strcpy(&OUTBUFFER[0], "AT+CMGF=1\r");
	       WriteCOM();
	       wait_for_response();
        }

	// SETTING COM MASK TO FORCE THE PORT TO INFORM THE USER ONLY 
	// IF IT RECEIVES ANY EVENTS FROM GSM MODEM
    
	//if(!SetCommMask(h_GSM, EV_RXCHAR | EV_CTS | EV_DSR | EV_RING | EV_RLSD)){
	if(!SetCommMask(h_GSM, EV_RXCHAR)){
		printf("Set Comm Mask Error!!!\n");
		return 0;
	}
	// IF WAIT COM EVENT FAILURE
	if (!WaitCommEvent(h_GSM, &dwEventMask, NULL)){
		printf("Wait Comm Event Error!!!\n");
		return 0;
	}
	
	//WAIT UNTIL EVENTS OCCURED IN THE PORT
	while(WaitCommEvent(h_GSM, &dwEventMask, NULL))	{
		
		// IF CHARACTER RECEIVED (EV_RXCHAR)
		if (dwEventMask & EV_RXCHAR){
			
			// READ THE OUTPUT OF PORT
			ReadCOM();
	 :sigh: 		
			int lenStrArray;
			int j = 0;
			
			// STORE BUFFER VALUES INTO STRING
			strArray = INBUFFER;
			lenStrArray = strArray.length();
			
			//POINTER DECLARED AS GLOBAL VARIABLE (SEE AT THE TOP)
			chrArray = (char*) realloc(chrArray,lenStrArray * sizeof(char));
			//chrArray = (char*) malloc(lenStrArray * sizeof(char));
			
			if (chrArray == NULL){
				printf("Memory allocation failed\n" );
				return 0;
			}
			
			// READ OUTPUT DATA ONE BY ONE TO ELIMINATE CARRIAGE RETURN CHARACTERS AND 
			// LINE FEED CHARACTERS AND TO EXTRACT ONLY VALID DATA
			for(int i = 0; i < lenStrArray; i++){
				/*
				if (Message_Store){
					if(strcat((char*)Message_Buffer[i], (char*)chrArray[i]) == 0){
						printf("Message store\n");
					}
				} */
				switch(strArray[i]){
				
					case '\x0A': //if line feed detected in the com output
						
						break;
					
					case '\x3E':
						
						greaterSign = true;
						printf("%d\n", greaterSign);
						break;
					case '\x0D': //if enter or carriage return detected in the com output
						
						chrArray[j] = '\0';
						int lenInput;
						lenInput = strlen(chrArray);
						
						if (lenInput> 0){
							printf("%s\n",	chrArray);
							ComEvent(chrArray);
							j=0;
						}
						
						break;
						
					default:
					
						chrArray[j] = strArray[i]; //Store the data one by one into buffer
						j++;
						
						break;
					}
			}
			
			free(chrArray);  // free memory
			chrArray = '\0'; // nullify the pointer
		}
	}
 CloseHandle(h_GSM); // Closing the Port
 h_GSM = INVALID_HANDLE_VALUE;
 return 0;
}
</time.h></windows.h></string>