#include "mbed.h"
#include<string>
#include "USBSerial.h"

#define max_inputLen 26  // define max length in one place not several.


Serial pc(USBTX, USBRX);

DigitalOut led1(LED1);
DigitalOut led2(LED2);
DigitalOut led3(LED3);

int main()
{
    int t;  // could have a narrower scope, could have a more meaningful name.
    char buff[max_inputLen +1];  // plus null terminator
    int code[max_inputLen];
    while(1) {

        // Completely optional couple of lines that I like to include.
        // These flush out any existing serial input before asking the user a question.
        // This prevents old data that's still in the buffer from getting mistaken for a
        //     user reply.
        while(pc.readable())
            pc.getc();


        pc.printf("\r\n Select drink!");

// Label and GOTO removed, it's considered bad practice and also in this case was unnecessary.
// since you're not doing anything other than looping waiting for a character there
// is no need for the if pc.readable(), just wait until there is data.

// revised serial reading, read one byte at a time until we get an end of line or too
// much data. Since we are already looping may as well convert to ints in the same loop.
        int index = 0;
        char keyIn = pc.getc();  // use getc and read one char at a time
        while ((index<max_inputLen)&&(keyIn!='\r')&&(keyIn!='\n')) { // check exit condition
            buff[index] = keyIn;        // store the text.
            code[index] = keyIn - '0';  // convert to an int.
            index++;                    // increase the index.
            keyIn = pc.getc();         // get the next character.
        }
        buff[index] = 0; // null terminate the input string.

        pc.printf("\r\n%s\r\n", buff); // echo the input back

        // your test code - this could go into a separate function to keep things cleaner

        if(code[1]==1 && code[2]==0 && code[3]==0)
            t = -1;
        else if(code[1]==0 && code[2]==1 && code[3]==0)
            t = 0;
        else if(code[1]==0 && code[2]==0 && code[3]==1)
            t = 1;
        else
            t = -2; // set a default so that if nothing matches we don't use the old value.

        // t=code[0]-code[1];    // -1 for juice   1 for shakes    0 for lemonade
        switch(t) {
            case 1 :
                pc.printf("\r\n Test successful for shakes");
                led1 = 1;
                wait(2);
                led1 = 0;
                break;
            case -1:
                pc.printf("\r\n Test successful for juices");
                led2 = 1;
                wait(2);
                led2 = 0;
                break;
            case 0 :
                pc.printf("\r\nTest successful for lemonades");
                led3 = 1;
                wait(2);
                led3 = 0;
                break;
            default:
                pc.printf("\r\n Test failed!");
                led1=1;
                led2=1;
                led3=1;
                wait(2);
                led1=0;
                led2=0;
                led3=0;
                break;
        }
        /* not needed
        buff[0] = '\0';
        memset(code, 0, sizeof(code));
        */
    }
}