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Update Factorial.java

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The factorial method can be simplified to 2 lines, which I believe is easier to read. Also, in previous version, if user enters two negative numbers back to back, the program crashes. We need a while loop to prompt the user until they actually enter the correct input, instead of only prompting them once. Also, if user enters a character instead of an integer, program crashes with no error message. We should fail more gracefully.
This commit is contained in:
MarcHines
2017-05-31 19:38:17 -04:00
committed by GitHub
parent 3907716e1f
commit 149e5d2abc
1 changed files with 26 additions and 29 deletions
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49
Factorial.java
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@ -1,10 +1,11 @@
package factorial;
import java.util.Scanner;
/**
* This program will print out the factorial of any non-negative
* number that you input into it.
*
* @author Unknown
* @author Marcus
*
*/
public class Factorial{
@ -15,23 +16,26 @@ public class Factorial{
* @param args Command line arguments
*/
public static void main(String[] args){
Scanner input = new Scanner(System.in);
//Prompt user to enter integer
System.out.print("Enter a non-negative integer: ");
Scanner input = new Scanner(System.in);
System.out.print("Enter a non-negative integer: ");
//Proceed with factorial calculation only if inputted number is not negative
if(input.hasNextInt()){
int number = input.nextInt();
if (number < 0){
System.out.print("Cannot execute. Please enter a non-negative integer: ");
number = input.nextInt();
} else {
//Output of factorial for any non-negative number
System.out.println("The factorial of "+number+" will yield: "+factorial(number));
}
}
input.close();
}
//If user does not enter an Integer, we want program to fail gracefully, letting the user know why it terminated
try{
int number = input.nextInt();
//We keep prompting the user until they enter a positive number
while(number < 0){
System.out.println("Your input must be non-negative. Please enter a positive number: ");
number = input.nextInt();
}
//Display the result
System.out.println("The factorial of " + number + " will yield: " + factorial(number));
}catch(Exception e){
System.out.println("Error: You did not enter an integer. Program has terminated.");
}
input.close();
}
/**
* Recursive Factorial Method
@ -40,14 +44,7 @@ public class Factorial{
* @return The factorial of the number
*/
public static long factorial(int n){
if (n==0){
return 1;
} else if (n==1){
return 1;
} else {
return n * factorial(n-1);
}
if(n == 0 || n == 1) return 1;
return n * factorial(n - 1);
}
}