java中使用for循环的阶乘

Question

 /* this program 
  * finds the factorial for any number
  */

public class forLoop1{

    public static void main(int x){    
        int init; 
        for( init = x; init < 2; init--){
            int finalint = init * --init; 
            System.out.println(finalint); 
        }
    }
}

^^ This program doesn't have an output, can anyone think of what's going wrong here? Any help would be appreciated, thank you!

Answer 1

If you want to use command line argument then parse String to int .

public static void main(String args[]) {
    int n=Integer.parseInt(args[0]);
    int fac = 1;
    for(int i = n; i >= 2; i--) {
        fac = fac * i;
    }
    System.out.println(fac);
}

You should run this program as java forLoop1 5 for an input 5 for example.

Answer 2

You have problems at -- ummmm -- almost each line. Have a look at the code below and trace each step with n = 4 (or any other number).

public class forLoop1{
  public static void main(String[] args){    
    // n is the number whose factorial is to be calculated
    int n = 10; 
    int factorial = 1;
    for(int i = n; i >= 2; i--){
      factorial = factorial * i;
    }
    System.out.println(factorial);
  }
}

Answer 3

import java.util.Scanner;

public class forLoop1{

 public static void main(String args[])
  { 
  System.out.println("Enter a number greater than zero.");
  Scanner in = new Scanner(System.in);

  int n = in.nextInt();
  in.close();

  int fact = 1;
  for (n = n; n>=2; n--)
    fact *= n;

  System.out.println("Factorial of "+n+" is = "+fact);
  }
}

This should work. will read user input.

In your code, the loop will only execute if init is 2 to start with.

Here is an explanation of the errors in your code:

public static void main(int x){ //Should be public static void main(String[] args)       
    int init; 
    for( init = x; init < 2; init--){ //Should be init >= 2
        int finalint = init * --init; //Possibly should be init * (init - 1)
                                      //In each iteration of the loop,      
                                      //finalint will be overwritten
    System.out.println(finalint); //This line is fine.
}

Answer 4

Thanks for the answers! Arjun, great your logic works perfectly A few things though: I do not need the (String[] args) part; I mentioned before too, as my IDE takes input for the x value by itself. So this is the code I used in the end:

  /* Factorial 
   * program
   */


public class forLoop2 {

    public void main(long x) { // long x is correct, as my IDE takes input through this 
        long fact = 1; 

        for( x = x; x >= 2; x--) 
            fact = fact * x; 

        System.out.println(fact); 
    }
}

Answer 5

import java.util.*;

public class forLoop1{
    public static void main(String args[]){ 

        Scanner input=new Scanner(System.in);
        System.out.println("Enter the number:");
        int x=input.nextInt();

        int finalint=1;
        for( int init=1;init<=x;init++){
            finalint=finalint*init;
        }
    }
}