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Thread: if else statement not working properly

  1. #1
    Junior Member tina G's Avatar
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    Unhappy if else statement not working properly

    help me in this code?
    my if else statement was not working properly?
    it always show valid?
    even the user put an invalid expression?
    what was i need to do? to solve it
    thanks in advance..
    import java.io.IOException;
    import java.io.*;
    import java.util.Arrays;
     
    public class datastruct {
     
     
      public static void main(String[] args) throws IOException {
     
     
      	BufferedReader A = new BufferedReader (new InputStreamReader(System.in));
      	String mathex;
      	String output = "";  
      	String out;
      	System.out.println("Enter a Mathematical Expresion:" );
    	mathex = A.readLine();
     
     
        int countOperators = 0;
        int countOperands = 0;
     
     
      for(int i = 0; i < mathex.length(); i++) {
         char ch = mathex.charAt(i);
         out = A.readLine();
     
     
         	 if(ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '%') {
           countOperators++;
     
     
         	if ( (out.equals("num"))){
     
    		System.out.println("invalid");
    	}
    	else if ( (out.equals("(")) || (out.equals("ch"))){	
     
    		System.out.println("valid");
    	}
    	else if ( (out.equals(")")) || (out.equals("ch"))){	
     
    		System.out.println("invalid");
    	}
    	else if ((out.equals ("(")) || (out.equals  ("ch"))){
     
    		System.out.println("valid");
    	}
    	else {
     
    		System.out.println("valid");
    	}
     
     
     
        System.out.println("INFIX is: " + mathex );
        System.out.println("POSTFIX is: " + mathex );
        System.exit(0);
     
         } 
         else
         countOperands++;
         }
     
        if((countOperators + 1) != countOperands || mathex.length() == 1){
          System.out.println("INVALID MATHEMATICAL EXPRESSION!!!!!"+ '\n');
        }
     
      	}
      }


  2. #2
    Member Faz's Avatar
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    Default Re: if else statement not working properly

    You shoudl try to make it more clear what you are trying to achieve with your programme and where exactly the problem is. I mean you have 3 If statements.

    	else if ( (out.equals("(")) || (out.equals("ch"))){	
     
    		System.out.println("valid");
    	}
    	else if ( (out.equals(")")) || (out.equals("ch"))){	
     
    		System.out.println("invalid");
    	}
    	else if ((out.equals ("(")) || (out.equals  ("ch"))){
     
    		System.out.println("valid");
    	}

    Would I be right in saying that the first and third ones there are the same? In which case drop the third one.

    Now if out is ch this will trigger the first condition so it will never go to the second one, I would assume that it can't be valid and invalid at the same time so what is it?

    A bit of debugging you could do would be to put some distinctive print statements inside the Ifs to see which ones are being triggered(or use IDE debugging).

  3. The Following User Says Thank You to Faz For This Useful Post:

    tina G (March 31st, 2010)

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