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POConverting infix expressions to postfix expressions
 

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  1. POConverting infix expressions to postfix expressions
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    <p>I have a problem i can't find the wrong in this function it sometimes do well with any input but it cached when there is parentheses in the input {i want to know where is the wrong in this code and how to fix it , and Is there another better way instead this way}</p> <pre><code> public static String Converting_infix_expressions_to_postfix_expressions(String infix) throws Exception{ StringTokenizer st = new StringTokenizer(infix); int numOF_tokens = st.countTokens(); String postfix = "" ; for (int i = 1; i &lt;= numOF_tokens; i++) { String term = st.nextToken(); try { // if it is an Float there is no problem will happen float x = Float.parseFloat(term); postfix += x +" " ; System.out.println("term is number " + term); } catch (Exception e) { System.out.println("term is symbol " + term); if(stack.isEmpty()) stack.push(term); else if(term == "(") stack.push(term); else if(term == ")"){ while((String)stack.peek() != "(") postfix += stack.pop() +" "; stack.pop(); } else{ int x = 0,y = 0; switch(term){ case "+": x = 1; break; case "-": x = 1; break; case "*": x = 2; break; case "/": x = 2; break; } switch((String)stack.peek()){ case "+": y = 1; break; case "-": y = 1; break; case "*": y = 2; break; case "/": y = 2; break; } if(x &gt; y) stack.push(term); else { int x1 = x , y1 = y; boolean puchedBefore = false; while(x1 &lt;= y1){ postfix += stack.pop() +" "; if(stack.isEmpty() || stack.peek() == "(" ){ stack.push(term); puchedBefore = true; break; } else{ switch(term){ case "+": x1 = 1; break; case "-": x1 = 1; break; case "*": x1 = 2; break; case "/": x1 = 2; break; } switch((String)stack.peek()){ case "+": y1 = 1; break; case "-": y1 = 1; break; case "*": y1 = 2; break; case "/": y1 = 2; break; } } } if(!puchedBefore) stack.push(term); } } } } while(!stack.isEmpty()){ postfix += stack.pop() +" "; } System.out.println("The postfix expression is : " + postfix); return postfix; } </code></pre>
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    1. USmohsen
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    1. COYou should use [`equals` instead of `==` when comparing strings](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java).
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      1. POConverting infix expressions to postfix expressions
      1. USassylias
    2. COHave you tried debugging? Get a case that you know fails and set a breakpoint, then step through to see where it is making a decision that doesn't make sense to you. Also, examples of expressions that work (and their output) and those that don't work (and their output) would help make this a better question.
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      1. USdigitaljoel
    3. COThere is quite a bit of repetition in the code... Did you consider writing a descending recursive parser instead?
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      1. POConverting infix expressions to postfix expressions
      1. USThomas Mueller
 

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