CODEWITHSUNDEEP
javainput
Sam
Sam

Reputation: 11

Get user input of positive integers in java

I have to write a program which asks a user to input integers, but they have to be positive. I'm pretty sure I have to use a loop, and don't think I'm allowed to use Math.abs().

What I've written right now looks quite messy though. Here is the code:

public class Q1{
    public static void main(String[] args){
        int num1, num2, num3;

        while(true){
            System.out.println("Input first integer.");
            num1 = TextIO.getInt();
            if(num1 > 0)
                break;
            System.out.println("Integer isn't positive. Try again");
        } 

        while(true){
            System.out.println("Input second integer.");
            num2 = TextIO.getInt();
            if(num2 > 0)
                break;
            System.out.println("Integer isn't positive. Try again");
       }

       while(true){
           System.out.println("Input third integer.");
           num3 = TextIO.getInt();
           if(num3 > 0)
               break;
           System.out.println("Integer isn't positive. Try again");
       }

....


   }
}

I've basically just done separate while loops for each integer to test if the integer is positive because when I use one loop I can't get it to run properly. Is there a way of just using one loop that will still work but looks much neater?

Upvotes: 0

Views: 8645

Answers (5)

blackSmith
blackSmith

Reputation: 3154

Here is a solution with a single while loop and using no array(it can be done). But, you can see that it's not upto the expectation. Such an implementation is always inefficient and is discouraged. So better use an array or separate method like others are suggesting. 

int i=0;
while (i < 3) {
        int tmp = 0;
        switch (i) {
        case 0:
            num1 = tmp = TextIO.getInt();
            System.out.println("Input first integer.");
            break;
        case 1:
            num2 = tmp = TextIO.getInt();
            System.out.println("Input second integer.");
            break;
        case 2:
            num3 = tmp = TextIO.getInt();
            System.out.println("Input Third integer.");
            break;
        }

        if (tmp < 0) {
            System.out.println("Integer isn't positive. Try again");
        } else {
            i++;
        }
    }

Upvotes: 0

ibreznik
ibreznik

Reputation: 169

Something like this perhaps?

public class Q1{
public static void main(String[] args){

int[] input_integers = new int[3]; //create an array of however many integers you need 

int i = 0; // initiate your counter
while(i<input_integers.length){ // you will loop through until all integers are set
System.out.println("Input integer number "+ (1+i)); // computers count from 0, humans from 1
input_integers[i] = TextIO.getInt();
if(input_integers[i] < 0) // check if it is not positive
System.out.println("Integer isn't positive. Try again");
else { // if it is, increment your counter and get the next integer
i++;
}
} 
 }

 }

Hope this helps

** This code was not tested

Upvotes: 0

Luke Taylor
Luke Taylor

Reputation: 9599

When programming you try and achieve 3 objectives: making your code, readable, intuitive and maintainable.

I would suggest you create a method you can reuse. The method in your case would look something like this:

public int readPositiveInt(String message) {
    int num = 0;
    boolean exitLoop = false;

    while(!exitLoop){
        System.out.println(message);
        num = TextIO.getInt();
        if(num > 0) {
            exitLoop = true;
            // I don't like to break from a while(true), I personally find it messy
        }
        else {
            System.out.println("Integer isn't positive. Try again");
        }

    } 

    return num;
}

Instead of creating variables like, num1, num2, num3 ... simply create an int array and store all values in there. If you are not sure how many numbers you would like to store, I suggest you use an implementation of a List, like the ArrayList.

I hope this helps.

Upvotes: 0

Michelle
Michelle

Reputation: 2900

You can wrap your while loop inside a for loop and put your integers in an array:

int[] nums = new int[] {-1, -1, -1};
for (int i = 0; i < 3; i++) {
  while(nums[i] <= 0)
    nums[i] = TextIO.getInt();
}

Upvotes: 0

Rohit Jain
Rohit Jain

Reputation: 213233

You can move that loop inside another method:

public int readPositiveInt() {
    int num = 0;
    int attempt = 0;
    int maxAttempt = 3;

    // Allow only maxAttempt to enter correct input.
    while(true && attempt < maxAttempt) {
        num = TextIO.getInt();
        if(num > 0)
            break;
        System.out.println("Integer isn't positive. Try again");
        ++attempt;
    } 

    return num;
}

And then call this method where ever you are having a loop currently.

Make sure TextIO, whatever it is, is available to this method.

Also, you should better enforce a maximum number of attempt, as you might go into an infinite loop, if user keeps on entering negative numbers.

Upvotes: 2

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