if statemens in java

[saeid jamali]

Hi everybody

As far as I know if statements are executed in the same order that they are coded(if true) so I am just wondering what happens if I have three if condition and the second condition is true first so it is executed and after that the first condition is true second? For example:
if(){   //Second true
}
if(){  //First true
}
if(){
}

I was coding a simple programme and I came across this issue if the first condition is true first then the programme works perfectly but if the second condition is true first then the first condition is ignored and is never checked again.

[Carey Brown]

In your example the 'if's would be processed in the order shown (top-down) and one 'if' is not dependent on any other 'if'.
If instead you wrote

if(){   //Second true
}
else if(){  //First true
}
else if(){
}

The first 'if' that was true would be processed and any following 'if's that might have been true as well will NOT be processed.

[Norm Radder]

if the second condition is true first then the first condition is ignored and is never checked again.

That implies to me that there could another thread of code that is changing the conditions while the code in the list of if statements is executing.  The condition for the first if is changed after the first if has executed.
Or do the statements controlled by the second if statement change the values for the condition used in the first if statement?

[Aqsa Anum]

Use if and else if statements. I hope you learnt it in C/C++ (IF you studied C/C++ before)
Good Luck

[saeid jamali]

the programme gets an input from the user and depending on the input it goes through one of the conditions and it this processes continuously repeats. If the first if statement is executed then the programme works fine with the second and third statement but if the second 'if statement' is executed then the first one is not executed anymore even if it is true. I tried it with both if and else if.

[Norm Radder]

if the second 'if statement' is executed then the first one is not executed anymore even if it is true.  

If the condition is true, the if statement's code block will be executed.  

Can you make a small complete program that compiles, executes and shows the problem?  What you say is happening must be caused by something else in the program.

[saeid jamali]

I think the problem is something else cause I tried it with while loop as well in a small version of the programme and it's the same

int rand;
		int num;
		Random random = new Random();
		Scanner input = new Scanner(System.in);
		
		rand = random.nextInt(100);
		System.out.println(rand);
		System.out.println("Please enter an number");
		num = input.nextInt();
		
		if(num > rand){
		while(num > rand){
			System.out.println("The num is GREATER ");
			System.out.println("Please enter a number");
			num = input.nextInt();
		 }
		}
		
		else if(num < rand){
		while(num < rand){
			System.out.println("the num is SMALLER");
			System.out.println("Enter a number");
			num = input.nextInt();
		 }
		}
	}

}

So if you enter a smaller number than the random number(Second condition true) followed by a greater number than the random number(First condition true) it crashes. On the other hand if the first condition is true followed by second condition it works perfectly

[Norm Radder]

Could you post the console from when you execute the program that shows the problem?  Add some comments to the print out explaining what the problem is.

[fred rosenberger]

it would also help if you posted a COMPLETE program. I should be able to cut-n-paste your code into a new file, compile it, and run it.  This is just a code snippet...there's no way to tell if maybe something else is going on or not.

And just saying "it crashes" doesn't help. If it crashes, it will print a stack dump...that's important information as well.

[Carey Brown]

Your while should be outside of your ifs.

import java.util.Random;
import java.util.Scanner;

public class Ifs
{
	public static void main( String[] args )
	{
		int rand;
		int num;
		Random random = new Random();
		Scanner input = new Scanner( System.in );

		rand = random.nextInt( 100 );
		System.out.println( rand );
		System.out.println( "Please enter an number" );
		num = input.nextInt();

		while( num != rand )
		{
			if( num > rand )
			{
			}
			else if( num < rand )
			{
			}
		}
	}
}

[saeid jamali]

Carey Brown wrote:Your while should be outside of your ifs.

import java.util.Random;
import java.util.Scanner;

public class Ifs
{
	public static void main( String[] args )
	{
		int rand;
		int num;
		Random random = new Random();
		Scanner input = new Scanner( System.in );

		rand = random.nextInt( 100 );
		System.out.println( rand );
		System.out.println( "Please enter an number" );
		num = input.nextInt();

		while( num != rand )
		{
			if( num > rand )
			{
			}
			else if( num < rand )
			{
			}
		}
	}
}

This solved the problem!
So could you please explain why my logic didn't work. I mean my logic also makes sense and theoretically it should work

  if(num > rand){
        while(num > rand){
            System.out.println("The num is GREATER ");
            System.out.println("Please enter a number");
            num = input.nextInt();
         }
        }
         
        else if(num < rand){
        while(num < rand){
            System.out.println("the num is SMALLER");
            System.out.println("Enter a number");
            num = input.nextInt();
         }
        }

I also tried the code below but it didn't work either without any if.
 
        

while(num > rand){
            System.out.println("The num is GREATER ");
            System.out.println("Please enter a number");
            num = input.nextInt();
         
        }
         
        
        while(num < rand){
            System.out.println("the num is SMALLER");
            System.out.println("Enter a number");
            num = input.nextInt();
         
        }

Could you please explain the difference between these logics please?
Thanks for your help

[Henry Wong]

saeid jamali wrote:
So could you please explain why my logic didn't work. I mean my logic also makes sense and theoretically it should work

It is easier to envision if you just draw it out. Take a pencil and paper, pretend you are the JVM, and follow the flow of the code as a diagrams. Keep track of the variables, the loops, the conditionals, and follow the code flow.

Henry

[Norm Radder]

What is the purpose of the code?  What value is it looking for?  Does there need to be an enclosing loop so that value is found?

[Carey Brown]

You could have written it this way but you still need the outer loop and this doesn't gain you anything and loses some clarity.

import java.util.Random;
import java.util.Scanner;

public class Ifs
{
	public static void main( String[] args )
	{
		int rand;
		int num;
		Random random = new Random();
		Scanner input = new Scanner( System.in );

		rand = random.nextInt( 100 );
		System.out.println( rand );
		System.out.println( "Please enter an number" );
		num = input.nextInt();

		while( num != rand )
		{
			while( num > rand )
			{
			}
			while( num < rand )
			{
			}
		}
	}
}