如何将占位符添加到随机 Int 然后从 Java 中的 Int 中提取一个数字？

Question

I am new to Java and programming all together.. I am trying to make a program that ciphers a number for the user. The user inputs 5 digits separately so I add them together to get a total. I need to pull the first digit and second digit of the total and enter it into (firstDigit+key)%10 and (secondDigit+key)%10. Then need to combine the answer to each equation together.

• My total needs to be two digits, so even if the user enters all 1's which would total to be 5, I need it to be displayed and seen as 05 so that both equations have a digit to use. It needs to be two digits. I cant seem to figure how to enter a place holder. I was thinking about trying to use:

   if (total < 10)

but then what?

• Secondly, the method I used below seems like a terrible way to pull a single digit from a number. I think I changed the int total into a string so I can use .substring to pull the digits, then converted back to an int. Surprisingly it works. Is there a better way to do this knowing that the number is random?

   String totalString = Integer.toString(total); String stringDigit1 = totalString.substring(0,1); String stringDigit2 = totalString.substring(1,2); int firstDigitInt1 = Integer.parseInt(stringDigit1); int firstDigitInt2 = Integer.parseInt(stringDigit2); int encodedDigit1 = (firstDigitInt1+key)%10; int encodedDigit2 = (firstDigitInt2+key)%10; System.out.println("Your encoded Number is: " + encodedDigit1 + encodedDigit2);

Answer 1

Your method for obtaining the individual digits is good, and if you want to maintain it I believe your intuition is correct, it should suffice to say:

if (total < 10) {
    firstDigitInt1 = 0
}

This will work out with your following math.

Your method with substrings is far from terrible, but in case you wanted something more sleek you can instead say:

int Digit1 = total / 10;
int Digit2 = total % 10;

Here, you can take advantage of integer truncation (where an integer won't remember decimal places) to get the first digit, which also solves the first problem: 5 / 10 = 0 (in terms of ints). For the second digit, it suffices to say modulo 10, as it is the remainder once the total is divided by 10.