can't initialize n with first input

Question sur la mission

Discussion en cours

Hello, I don't understand what's wrong here. If I initialize int n = 0 then it's not taking the first input into account. But if I initialize it with Integer.parseInt(lecteur.readLine()) my code crashes at l.17 with the error java.lang.NumberFormatException: For input string: "" as if it couldn't parse correctly.

Écris un programme qui :
1. lit un nombre n (qui doit être supérieur à 0) dans la console
2. lit n nombres dans la console
3. Affiche le plus grand des n nombres saisis.

Impératifs :

Le programme doit lire les nombres au clavier.
Le programme doit afficher un nombre à l'écran.
La classe doit avoir une méthode public static void main.
N'ajoute pas de nouvelles méthodes à la classe Solution.
Le programme doit afficher le plus grand des n nombres saisis.
Le programme ne doit rien afficher si n est inférieur ou égal à 0.

package fr.codegym.task.task05.task0532; import java.io.*; /* Mission sur les algorithmes */ public class Solution { public static void main(String[] args) throws Exception { BufferedReader lecteur = new BufferedReader(new InputStreamReader(System.in)); int maximum = 0 ; int n = Integer.parseInt(lecteur.readLine()); int inputNumber = 0; while(!lecteur.readLine().equals("")) { inputNumber = Integer.parseInt(lecteur.readLine()); if ( inputNumber > 0 && inputNumber > n) { n = inputNumber; } } if(n>0) { maximum = n; System.out.println(maximum); } } }

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Thomas

niveau Bayreuth, Bayreuth, Germany

24 février, 00:27

You read to often a line from the console. First you wait for an input in line 13. That's OK. The program is supposed to read a number n and then loop n times (reading n numbers). What you however do then is looping till an empty string is entered. That's not what the task is about. And you even do it wrong as you read a line in line 16, check for emtpy and then you throw the entered string away. In line 17 you read a new string and do something. As said, that's not what the task is asking. The problem you experience is related to that multiple readLine calls. Imagine an input 2, 3, emptyString... The first read saves the result in n. The second read in line 16 checks if the input is not the empty string. That's not the case and we enter the loops body. Here you enter now an empty string and the parseInt method errors out as it can not convert an empty string to an integer. One possible approach would be (without using lists, arrays or Integer.MAX_VALUE and I didn't reuse your variable names as I don't feel confident with the French language):

BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
int n = Integer.parseInt(console.readLine()); // enter a number n

if (n > 0) { // if n > 0 enter n numbers and display the max of these n numbers
    int input, max = Integer.parseInt(console.readLine());

    for (int i = 1; i < n; i++) {
        input = Integer.parseInt(console.readLine());
        if (input > max) {
            max = input;
        }
    }
    System.out.println(max);
}