File content as of revision 2:690dd6bdb9a7:

//http://www.cplusplus.com/reference/cstring/strcmp/

#include "mbed.h"
#include <iostream>
#include <string> 
#include <stdio.h>
#include <ctype.h>

//Digital outputs
DigitalOut onBoardLED(LED2);
DigitalOut redLED(PE_15);
DigitalOut yellowLED(PB_10);
DigitalOut greenLED(PB_11);

char rxBuffer[80];

char i = 0;
char c = 0;

string key = "apple";


RawSerial pc(USBTX, USBRX, 9600);
Thread serialRX(osPriorityNormal);

// Rx Interupt routine
void Rx_interrupt(){
    pc.attach(NULL, Serial::RxIrq);     // Disable Rx interrupt
    serialRX.signal_set(0xA);                   // Set signal for Rx thread
}

// Read received chars from UART
void rx_thread(){
    while (true) {
        Thread::signal_wait(0xA);
        Thread::signal_clr(0xA);
        //memset(rxBuffer, 0, sizeof(rxBuffer));
        while (pc.readable()) {
            c = pc.getc();
            rxBuffer[i] = c; 
            i = i + 1;
            yellowLED = !yellowLED;
        }
        
        pc.attach(&Rx_interrupt);         // Enable Rx interrupt
        redLED = !redLED;
        
   
        
        if (c == '\r') {
            greenLED = !greenLED;
            string rxBufferSTR = rxBuffer;
            int c = rxBufferSTR.length();
            rxBuffer[c-1] = NULL;           // CR character. Probably not needed
            //string str(rxBuffer);
            //printf("rxBuffer: %s\n", rxBuffer);
            //printf("rxBuffer is %u characters long\n", (unsigned)strlen(rxBuffer));

            if (rxBufferSTR.find(key) != string::npos) {
                pc.printf("Found");
            }
            /*
            if (strcmp (key,rxBuffer) == 0) {
                puts ("Apple is delicious!\n");

                pc.printf ("The command entered is %u characters long.\n",(unsigned)strlen(key));
                int i =0;
                int keysize = (unsigned)strlen(key);
                int endfor = keysize;

                //check for number here

                for(i=0; i<10; i++) {
                    pc.printf("%c", rxBuffer[i]);
                }

            } else {
                puts ("try again loser!\n");
            }
            */
            
            memset(rxBuffer, 0, sizeof(rxBuffer)); //only reset after strcmp
            i = 0;
        }
  }
    
}


int main() {
    
    serialRX.start(rx_thread);      //start serial interrupt thread
    pc.attach(&Rx_interrupt);           //attach interrupt function that triggers when data is available
    
    while(1) {
        Thread::wait(2500);
    }
    
}