Can you use a for loop inside the condition of an if-else statement?

Question

Can you use a for loop inside the condition of an if-else statement? For example, something like this...

if(
        for(q = 0; q < 10; q++){
            values[q]>=values[q+1];
        }          
            )

            {

         done = 0;
    }

This is loading an error I can't seem to place. I want the if statement to check to see if the int[] I called values is in order from greatest to least, and if it is, set int variable done equal to 0.

I only just started taking a programming class and I bet this is a very dumb mistake, but I've been trying to figure this out for a while and some help would be absolutely fantastic.

Answer 1

You should work out your condition first (ie is your array in order), and then feed that in to your if statement. Like so...

boolean isOrdered = true;

for(q = 0; q < 10; q++){
  if (values[q]>=values[q+1]){
    // in order
    }
  else {
    // not in order
    isOrdered = false;
    break; // we have found a false, so we can quit out of the for loop
    }
  }

if (isOrdered){
  // do something if the array is in order;
  }

Answer 2

You can do it if you refactor the logic into a method that returns a boolean:

if (isInOrder(values)) {
    //
}

private static boolean isInOrder(int[] array) {
    for (int i = 0; i < array.length - 1; i++)
        if (array[i] > array[i+1])
            return false;
    return true;
}

Answer 3

A for loop can exist inside of an if block

if (true) {
    for (int i = 0; i < 5; i++) {
        System.out.println("Hello, World!");
    }
}

But a for loop can not be the condition of the if block

if( for (int i = 0; i < 5; i++) { } ) { }

A for loop is not a boolean. Every if condition requires a boolean.

Answer 4

No . If requires a boolean test. For loop doesn't return a boolean value. You can instead separate the check into another function.

if( isArrayOrdered(values) ){
    done = 0;
}

// assuming values is an array of `int` values
private boolean isArrayOrdered( int[] values){
   for(int q = 1; q < values.length; q++){ 

      if( values[q] > values[q-1] ){
         return false;
      }
   }

   return true;
}

Answer 5

No, you can't. The if condition must evaluate to some boolean value, which doesn't happen with this for loop.

It can only be in the if statement body, like

if(someCondition)
    for(int i = 0;i < 10;i++)...

To achieve your goal, a code like this one might help:

boolean ordered = true;

for(int i = 0;i < array.length - 1;i++) {
    if(array[i] > array[i+1]) {
        ordered = false;
        break;
    }
}

if(ordered) // your if body here

Answer 6

The expression inside the "if" condition should evaluate to a boolean or Boolean otherwise the code will not compile.

Check that Java specs page here

Answer 7

I think you probably want the alternate nesting, and start with the assumption that done = 0 (that is, that the list is correctly ordered), unless you prove in the loop that it is not true.

public class Play{
    public static void main(String[] args) {
        done = 0;
        for(q = 1; q < 10; q++){
            if (values[q-1]<values[q]) {
                  done = 1;
                  break;
             }   

        }          


    }
}

Answer 8

You need to break you logic down into steps.

first of all, a method

boolean isInOrder (int [] values) {

    for(int q = 0; q < values.length - 1; q++){

        if (values[q] > values[q+1]) {
          return false; 
        }
   }
   return true;
}

// now lets call this method

  if (isInOrder (values)) {
     System.out.println ("In Order");
  }
  else {
     System.out.println ("Not In Order");
  }

Answer 9

将“for 循环”语句放在 if 语句“(”和“)”之间是不可能的。但是如果你在 if 语句“{”和“}”之间写“for 循环”是可能的。谢谢