Read time digits from DS1307 and run code based on return

Question

I am currently reading a DS1307 adafruit breakout board and I need to drive two nixie tubes from a shift register. The shift register is running two 74141 IC chips. I have code that loops through all the nixie digits one at a time with a delay of 1 second between each. Now I need to write some code to pull min, hour, and second and change the shift register low/high outputs to display the correct nixie digit. I have the DS1307 returning the correct time on my com by using

 Serial.print(now.hour(), DEC);
 Serial.print(now.minute(), DEC);
 Serial.print(now.second(), DEC);

However, I am not sure how to dimension a string, set that string equal to the two digits on the hour, minute, or time, and then divide the two digits and write if statements to correctly display the tubes. I am used to VB.NET and now C coding.

=======================UPDATE=======================

I am using this code to set any individual digit of the nixie tube to on.

       //Turn on 0
 sr.set(4, LOW);
 sr.set(5, LOW);
 sr.set(6, LOW);
 sr.set(7, LOW);

The sr is the shift register and each number is which leg of the shift register I am turning low or high. This specific piece turns on the digit 0.

Answer 1

You can set up an array containing the bit patterns to turn on different digits, and then use code that sends the bits for the high digit of now.hour()/12 and the bits for the low digit of now.hour()%12. For example:

const byte digiBits[] = { B0000, B0001, 
// and so forth for all the digits ...
};

void send1Digit(byte digiVal, byte whichDigit) {
  // somehow use whichDigit to direct the bits someplace...

  // To send the bits:
  byte bits = digiBits[digiVal];
  for (byte i=4; i<8; ++i) {
    sr.set(i, bits & 1);  // Set a bit in SR to 0 or 1
    bits >>= 1; // shift out the used bit
  }
}

void send2Digits(byte numVal, byte whichDigit) {
  send1Digit(numVal/10, whichDigit);
  send1Digit(numVal%10, whichDigit+1);
}

void loop() {
  // other stuff, then:
  send2Digits(now.hour(), HourSpot);
  send2Digits(now.minute(), MinuteSpot);
  send2Digits(now.second(), SecondSpot);
  // other stuff ...
}

Note 1: If your sr.set() routine is doing any complicated masking or shifting, you may be able to avoid some of that by ORing digiBits[digiVal] with whatever number sr.set() might be building up to shift out.

Note 2: If the numerical value of digiBits[digiVal] is equal to digiVal, then don't bother defining digiBits[], but instead in send1Digit() just say byte bits = digiVal, or use digiVal directly in place of bits.