程序只会输出else语句

Question

I'm working on creating a linear search in Java using the StdIn library from Princeton, and I can't figure out why my if-else statement will only print out “-1”.

It seems to me that its skipping over the if block entirely and going straight onto the else . I'm entering in my list with command-line arguments and ending the list by pressing control-d (not sure what it is on windows, sorry). Any help at all would be greatly appreciated.

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

        if (args[0].equals("linear")) {
            int n = Integer.parseInt(args[1]);
            LinearSearch(n);
        }
        else {
            System.out.println("Please enter linear");
        }
   }

   public static void LinearSearch(int n) {
       int x = -1;
       //int u = -1;
       int c, search, array[];
       int value = StdIn.readInt(); //input values
       array = new int[value]; //array list

       while (x < 0) {
           //System.out.println(n);
           //System.out.println("linear");

           //loop to populate array list
           for(c = 0; c < value; c++)
              array[c] = StdIn.readInt();  


           //loop to search for "n"
           for (c = 0; c < value; c++) {
               if(array[c] == n){
                   System.out.println(n + " is at index " + c);
                   x++;
                   return;
               }
               else{
                   continue;
               }
           }

            System.out.println("-1");
            x++;
        }
    }
}

Edit: I updated the entire LinearSearch(n) method. It now finds the value from the list that I enter and gives me the value of -1 when the value is not there. The problem now is that the ArrayList only populates to whatever the first number I enter is when I need to populate to however many int s are entered in the command-line argument

Answer 1

Your method will return (after printing -1) as soon as the searched value is not in the array:

    else{
        System.out.println("-1");
        return;  // EXITING HERE
    }

so if the value entered is not the the first value in the array, you will get -1 and the method is terminated.

What you probably want is to return (after printing) as soon as the value IS FOUND, or continue searching up to the last array entry. After this loop exists, that is, nothing was found, you want to print -1 (and return/terminate).

Something like

loop array {
    if value is equal array entry {
        print message
        return
    }
    // else continue looping
}
print -1

Answer 2

Finally after lots of effort I have completed your code.

Run program as follows java SearchAlgs 4 5 6 7

enter size:5

67546

Output would be :

6 is at index 2
7 is at index 3
5 is at index 1
4 is at index 0

Code: import java.util.Scanner; class SearchAlgs {

    public static void main(String[] args) {
        int list[]=new int[(args.length)-1];
        int conv=0;
        if (args[0].equals("linear")){
            for(int i=0;i<(args.length-1);i++)
            {
                conv=Integer.parseInt(args[i+1]);
                list[i]=conv;
            }
            LinearSearch(list);
        }
        else{
            System.out.println("Please enter linear");
        }
   }


public static void LinearSearch(int n[]){
    int x = -1;
    int c, search, array[];
    Scanner reader = new Scanner(System.in);  // Reading from System.in
    System.out.print("Enter size:");
    int size = reader.nextInt();
    array = new int[size]; //array list

   while (x < 0){
       //loop to populate array list
           for(c = 0; c < size; c++)
              array[c] = reader.nextInt();  

       //loop to search for "n"
       for (c = 0; c < n.length; c++){
            for(int z=0; z<n.length;z++){
               if(array[c] == n[z]){
                   System.out.println(n[z] + " is at index " + z);
                   x++;
               }
               else{
                   continue;
               }
           }
       }
         x++;

   }
}
}