如何引用用户输入的int？

Question

Easy question (I'm a beginner!)... My java program needs to refer back to the user-entered integers stored as variables "a" and "z". These two variables are initialized using a Scanner and the nextInt() method. Here's my code:

Scanner in = new Scanner(System.in);
    int a;
    int z;
    int x;

    System.out.println("Please provide a lower bound (integer): ");
    a = in.nextInt();

    System.out.println("Please provide an upper bound (integer): ");
    z = in.nextInt();

So now I need to refer back to these user-entered variables in a for-loop that appears later on, but I do not know the syntax to do this. I need the for-loop to start at "a" and continue one-by-one until "z".

for(a ; a <= z ; a++) {
    //code irrelevant to my question
}

Java is making it very clear that I cannot just write the variables in the for-loop, so how do I do it? Thanks!

Answer 1

You want to do that with a loop counter, let it be i :

for (int i = a; i <= z; i++) {
    //process i
}

In this way you have i that starts at a and increases up to z .

Answer 2

To start at a and end on z, inclusive:

for(; a <= z ; a++) {

To stop right before z:

for(; a < z ; a++) {

This will change the variable a .

You don't need to fill that space before the first semi-colon. That's the "initialize counter" spot, and you've already initialized your counter from user input above (before) the loop.

If you don't want a to change, then simply duplicate its value into a temporary one, as in @skiwi's answer:

for(int i = a; i <= z; i++)  {

Here's some good information: https://www.google.com/search?q=for+loop+java

Answer 3

If you want to include z:

for(int i=a;i<=z;i++){
    [stuff]
}

or, if you want it to exclude z:

for(int i=a;i<z;i++)
    [stuff]
}

This is because the format for for loops is for(int [counter]=[start value];[counter][condition][limit];[counter][change amount]) . For example, if you wanted something to loop up to (including) two, including zero, your code would be for(int i=0; i<3;i++) , while if you wanted it to loop down from two to zero it would be for(int i=2; i>=0;i--) . To make the loop skip values just change the amount the counter increases/decreases by, such as i+=2 , or i-=2

Answer 4

Existing answers tell you how to fix it, but don't explain what the problem is. If you try to compile the class, you'll see the following error

$ javac SomeClass.java
SomeClass.java:16: error: not a statement
for(a ; a <= z ; a++) {
^

That's because a by itself is not a statement.

The simplest thing is to just omit the a since you don't need to initialize it

for(; a <= z ; a++) {}

Alternatively, you could create a looping variable so you don't affect a and you can initialize it in the loop so it looks more like a normal loop.

for(int i = a; i <= z ; i++) {}