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Nov 11th, 2006
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help with a infix to postfix program

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I have this program but need to adjust a little bit. At first it asks to enter an expression but I can only enter it in this form -> 7*(23-2)+10
but i want to enter it like this -> 7 * (23- 2)+ 10;
therefore the program should ignore the spaces and semicolon. also if i enter only the semicolon it should exit the program.
Also i can't get the program to restart and ask the enter the expression thing. please help me!!!!! thanks 





  1. #include <iostream>
  2.  #include <string>
  3.  #include <stdlib.h>
  4.  #include <conio.h>
  5.  #include <math.h>
  6.     using namespace std;
  7.  
  8.  //-----------------  Declaration of Constant Variable  ------------------//
  9.  
  10.  const int max_length=10;
  11.  
  12.  //------------------------  Class Definition  ---------------------------//
  13.  
  14.  class Evaluator
  15.     {
  16.        private:
  17.       char infix_expression[25][6];
  18.       char postfix_expression[25][6];
  19.  
  20.       char char_stack[max_length];
  21.       long int_stack[max_length];
  22.  
  23.       int int_top;
  24.       int char_top;
  25.  
  26.       int postfix_rows;
  27.       int infix_rows;
  28.  
  29.       int input_characters_count;
  30.  
  31.        public:
  32.       char char_pop( );
  33.  
  34.       long int_pop( );
  35.  
  36.       void set_initial_values( );
  37.       void get_infix_expression( );
  38.       void char_push(char);
  39.       void show_infix_to_postfix_convertion( );
  40.       void int_push(long);
  41.       void show_evaluation_of_postfix_expression( );
  42.     };
  43.  
  44.  //----------------------  Function Definitions  -------------------------//
  45.  
  46.  
  47.  //----------------------  set_initial_values( )  ------------------------//
  48.  
  49.  
  50.  void Evaluator::set_initial_values( )
  51.     {
  52.        int_top=-1;
  53.        char_top=-1;
  54.        infix_rows=0;
  55.        postfix_rows=0;
  56.  
  57.        for(int count_1=0;count_1<max_length;count_1++)
  58.       {
  59.          int_stack[count_1]=0;
  60.          char_stack[count_1]=NULL;
  61.       }
  62.  
  63.        for(int count_2=0;count_2<25;count_2++)
  64.       {
  65.          strset(infix_expression[count_2],NULL);
  66.          strset(postfix_expression[count_2],NULL);
  67.       }
  68.     }
  69.  
  70.  /*************************************************************************/
  71.  //-----------------------  get_infix_expression( )  ---------------------//
  72.  /*************************************************************************/
  73.  
  74.  void Evaluator::get_infix_expression( )
  75.     {
  76.        Input:
  77.        system("cls");
  78.  
  79.        set_initial_values( );
  80.  
  81.        int flag=0;
  82.        int count_1=-1;
  83.        int number_length=0;
  84.        int operand_count=0;
  85.        int operator_count=0;
  86.        int expression_right_wrong=1;
  87.        int input_characters_count=0;
  88.        int left_parenthesis_count=0;
  89.        int right_parenthesis_count=0;
  90.  
  91.        char temp_expression[5]={NULL};
  92.  
  93.        cout<<"\n\n\n\t Enter the Infix Expression : "<<endl;
  94.  
  95.        do
  96.       {
  97.          temp_expression[0]=getch();
  98.  
  99.  
  100.          if(int(temp_expression[0])!=8)
  101.         cout<<temp_expression;
  102.  
  103.  
  104.          if((int(temp_expression[0])>=48 &&
  105.                 int(temp_expression[0])<=57) && number_length<5)
  106.         {
  107.            if(flag==0)
  108.               {
  109.              count_1++;
  110.              flag=1;
  111.              operand_count++;
  112.  
  113.              strcpy(infix_expression[count_1],temp_expression);
  114.               }
  115.  
  116.            else if(flag==1)
  117.               strcat(infix_expression[count_1],temp_expression);
  118.  
  119.            number_length++;
  120.         }
  121.  
  122.          else if( temp_expression[0]=='^' || temp_expression[0]=='/'
  123.            || temp_expression[0]=='*' || temp_expression[0]=='-'
  124.            || temp_expression[0]=='+' || temp_expression[0]=='('
  125.                           || temp_expression[0]==')')
  126.         {
  127.            flag=0;
  128.            count_1++;
  129.            number_length=0;
  130.  
  131.            strcpy(infix_expression[count_1],temp_expression);
  132.  
  133.            if(temp_expression[0]=='(')
  134.               left_parenthesis_count++;
  135.  
  136.            else if(temp_expression[0]==')')
  137.               right_parenthesis_count++;
  138.  
  139.            else
  140.               operator_count++;
  141.         }
  142.  
  143.          if(int(temp_expression[0])==8 && count_1>=0)
  144.         {
  145.            int length = strlen(infix_expression[count_1]);
  146.  
  147.            for(int count_2=0;count_2<length;count_2++)
  148.               cout<<char(8)<<" "<<char(8);
  149.  
  150.            if(int(infix_expression[count_1][0])>=48 &&
  151.                        int(infix_expression[count_1][0])<=57)
  152.               operand_count--;
  153.  
  154.            else if(infix_expression[count_1][0]=='^' ||
  155.                    infix_expression[count_1][0]=='/' ||
  156.                   infix_expression[count_1][0]=='*' ||
  157.                      infix_expression[count_1][0]=='-' ||
  158.                     infix_expression[count_1][0]=='+' )
  159.               operator_count--;
  160.  
  161.            else if(infix_expression[count_1][0]=='(')
  162.               left_parenthesis_count--;
  163.  
  164.            else if(infix_expression[count_1][0]==')')
  165.               right_parenthesis_count--;
  166.  
  167.            strset(infix_expression[count_1],NULL);
  168.  
  169.            flag=0;
  170.            count_1--;
  171.            input_characters_count--;
  172.         }
  173.  
  174.          if(int(temp_expression[0])==13)
  175.         break;
  176.  
  177.          else if(int(temp_expression[0])==27)
  178.         {
  179.            infix_expression[25][6]='$';
  180.  
  181.            break;
  182.         }
  183.  
  184.          else if(operand_count<operator_count)
  185.         {
  186.            infix_expression[25][6]='$';
  187.  
  188.            break;
  189.         }
  190.  
  191.          else if(!left_parenthesis_count && right_parenthesis_count)
  192.         {
  193.            count_1++;
  194.  
  195.            break;
  196.         }
  197.  
  198.          else if(temp_expression[0]!='^' && temp_expression[0]!='/' &&
  199.               temp_expression[0]!='*' && temp_expression[0]!='-' &&
  200.               temp_expression[0]!='(' && temp_expression[0]!=')' &&
  201.               temp_expression[0]!='+' && temp_expression[0]!='0' &&
  202.               temp_expression[0]!='1' && temp_expression[0]!='2' &&
  203.               temp_expression[0]!='3' && temp_expression[0]!='4' &&
  204.               temp_expression[0]!='5' && temp_expression[0]!='6' &&
  205.               temp_expression[0]!='7' && temp_expression[0]!='8' &&
  206.               temp_expression[0]!='9' && int(temp_expression[0])!=8
  207.                          && int(temp_expression[0])!=27 )
  208.         {
  209.            infix_expression[25][6]='$';
  210.  
  211.            break;
  212.         }
  213.  
  214.          input_characters_count++;
  215.       }
  216.        while(count_1<=22 && input_characters_count<=24);
  217.  
  218.        if(operator_count!=(operand_count-1))
  219.       expression_right_wrong=0;
  220.  
  221.        else if(left_parenthesis_count!=right_parenthesis_count)
  222.       expression_right_wrong=0;
  223.  
  224.        else if(count_1<2)
  225.       expression_right_wrong=0;
  226.  
  227.        else if(infix_expression[25][6]=='$')
  228.       expression_right_wrong=0;
  229.  
  230.        if(expression_right_wrong==0)
  231.       {
  232.          cout<<"\n\n\t Input Expression is not correct."<<endl;
  233.  
  234.          goto Input;
  235.       }
  236.  
  237.        infix_rows=(count_1+1);
  238.     }
  239.  
  240.  /*************************************************************************/
  241.  //---------------------------  int_push( )  -----------------------------//
  242.  /*************************************************************************/
  243.  
  244.  void Evaluator::int_push(long item)
  245.     {
  246.        int_top++;
  247.        int_stack[int_top]=item;
  248.     }
  249.  
  250.  /*************************************************************************/
  251.  //---------------------------  int_pop( )  ------------------------------//
  252.  /*************************************************************************/
  253.  
  254.  long Evaluator::int_pop( )
  255.     {
  256.        long item=0;
  257.  
  258.        item=int_stack[int_top];
  259.        int_stack[int_top]=0;
  260.        int_top--;
  261.  
  262.        return item;
  263.     }
  264.  
  265.  /*************************************************************************/
  266.  //--------------------------  char_push( )  -----------------------------//
  267.  /*************************************************************************/
  268.  
  269.  void Evaluator::char_push(char item)
  270.     {
  271.        char_top++;
  272.        char_stack[char_top]=item;
  273.     }
  274.  
  275.  /*************************************************************************/
  276.  //--------------------------  char_pop( )  ------------------------------//
  277.  /*************************************************************************/
  278.  
  279.  char Evaluator::char_pop( )
  280.     {
  281.        char item=0;
  282.  
  283.        item=char_stack[char_top];
  284.        char_stack[char_top]=NULL;
  285.        char_top--;
  286.  
  287.        return item;
  288.     }
  289.  
  290.  /*************************************************************************/
  291.  //-----------------  show_infix_to_postfix_convertion( )  ---------------//
  292.  /*************************************************************************/
  293.  
  294.  void Evaluator::show_infix_to_postfix_convertion( )
  295.     {
  296.        char_push('(');
  297.        strcpy(infix_expression[infix_rows],")");
  298.  
  299.        int count_1=0;
  300.        int count_2=0;
  301.  
  302.        do
  303.       {
  304.          char symbol_scanned[10]={NULL};
  305.  
  306.          strcpy(symbol_scanned,infix_expression[count_1]);
  307.  
  308.          if(symbol_scanned[0]=='(')
  309.         char_push(symbol_scanned[0]);
  310.  
  311.          else if(symbol_scanned[0]==')')
  312.         {
  313.            char temp[5]={NULL};
  314.  
  315.            while(char_stack[char_top]!='(')
  316.               {
  317.              temp[0]=char_pop( );
  318.  
  319.              strcpy(postfix_expression[count_2],temp);
  320.  
  321.              count_2++;
  322.               }
  323.  
  324.             temp[0]=char_pop( );
  325.         }
  326.  
  327.          else if(symbol_scanned[0]=='/' || symbol_scanned[0]=='*' ||
  328.                symbol_scanned[0]=='-' || symbol_scanned[0]=='+'
  329.                            || symbol_scanned[0]=='^')
  330.         {
  331.            if(symbol_scanned[0]=='^')
  332.               {
  333.               }
  334.  
  335.            else if(symbol_scanned[0]=='*' || symbol_scanned[0]=='/')
  336.               {
  337.              while(char_stack[char_top]=='^' ||
  338.                     char_stack[char_top]=='*' ||
  339.                            char_stack[char_top]=='/')
  340.                 {
  341.                 char temp[5]={NULL};
  342.  
  343.                 temp[0]=char_pop( );
  344.                 strcpy(postfix_expression[count_2],temp);
  345.  
  346.                 count_2++;
  347.                 }
  348.               }
  349.  
  350.            else if(symbol_scanned[0]=='+' || symbol_scanned[0]=='-')
  351.               {
  352.              while(char_stack[char_top]!='(')
  353.                 {
  354.                 char temp[5]={NULL};
  355.  
  356.                 temp[0]=char_pop( );
  357.                 strcpy(postfix_expression[count_2],temp);
  358.  
  359.                 count_2++;
  360.                  }
  361.               }
  362.  
  363.            char_push(symbol_scanned[0]);
  364.         }
  365.  
  366.          else if(symbol_scanned[0]!='/' || symbol_scanned[0]!='*' ||
  367.              symbol_scanned[0]!='-' || symbol_scanned[0]!='+' ||
  368.              symbol_scanned[0]!='(' || symbol_scanned[0]!=')' ||
  369.                               symbol_scanned[0]!='^')
  370.         {
  371.            strcpy(postfix_expression[count_2],symbol_scanned);
  372.  
  373.            count_2++;
  374.         }
  375.  
  376.          count_1++;
  377.       }
  378.        while(char_stack[char_top]!=NULL);
  379.  
  380.        postfix_rows=count_2;
  381.  
  382.        cout<<"\n\n\t Postfix Expression is : ";
  383.  
  384.        for(int count_3=0;count_3<postfix_rows;count_3++)
  385.       cout<<postfix_expression[count_3]<<" ";
  386.  
  387.        cout<<endl;
  388.     }
  389.  
  390.  /*************************************************************************/
  391.  //------------  show_evaluation_of_postfix_expression( )  ---------------//
  392.  /*************************************************************************/
  393.  
  394.  void Evaluator::show_evaluation_of_postfix_expression( )
  395.     {
  396.        int count=0;
  397.  
  398.        char symbol_scanned[10]={NULL};
  399.  
  400.        strcat(postfix_expression[postfix_rows],"=");
  401.  
  402.        do
  403.       {
  404.          strset(symbol_scanned,NULL);
  405.          strcpy(symbol_scanned,postfix_expression[count]);
  406.  
  407.          count++;
  408.  
  409.          if(symbol_scanned[0]=='/' || symbol_scanned[0]=='*' ||
  410.         symbol_scanned[0]=='-' || symbol_scanned[0]=='+' ||
  411.                              symbol_scanned[0]=='^')
  412.         {
  413.            long value_1=0;
  414.            long value_2=0;
  415.            long result=0;
  416.  
  417.            value_1=int_pop( );
  418.            value_2=int_pop( );
  419.  
  420.            switch(symbol_scanned[0])
  421.               {
  422.              case '+': result=value_2+value_1;
  423.                    break;
  424.  
  425.              case '/': result=value_2/value_1;
  426.                    break;
  427.  
  428.              case '*': result=value_2*value_1;
  429.                    break;
  430.  
  431.              case '-': result=value_2-value_1;
  432.                    break;
  433.  
  434.              case '^': result=powl(value_2,value_1);
  435.                    break;
  436.               }
  437.  
  438.            int_push(result);
  439.         }
  440.  
  441.          else if((symbol_scanned[0]!='/' || symbol_scanned[0]!='*' ||
  442.               symbol_scanned[0]!='-' || symbol_scanned[0]!='+' ||
  443.                symbol_scanned[0]!='^' )&& symbol_scanned[0]!='=')
  444.  
  445.         {
  446.            long number=atol(symbol_scanned);
  447.  
  448.            int_push(number);
  449.         }
  450.       }
  451.        while(symbol_scanned[0]!='=');
  452.  
  453.        cout<<"\n\n\t Result of Postfix Expression Evaluation : ";
  454.        cout<<int_stack[0];
  455.        getch( );
  456.  
  457.     }
  458.  
  459.  //----------------------------  main( )  --------------------------------//
  460.  
  461.  int main( )
  462.     {
  463.        system("cls");
  464.  
  465.        Evaluator obj;
  466.  
  467.        obj.get_infix_expression( );
  468.        obj.show_infix_to_postfix_convertion( );
  469.        obj.show_evaluation_of_postfix_expression( );
  470.  
  471.        return 0;
  472.     }
Last edited by taruj83; Nov 11th, 2006 at 1:25 am.
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taruj83 is offline Offline
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Nov 11th, 2006
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Re: help with a infix to postfix program

In your in[ut function, if you get one of the characters you want to ignore, just go back and input another character. It's just an addition to your already complex input loop.
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Re: help with a infix to postfix program

>this form -> 7*(23-2)+10
but i want to enter it like this -> 7 * (23- 2)+ 10;

So create a method which strips it of whitespace. Or do you mean it crashes when you use spaces? If so use cin.getline() instead.

>also if i enter only the semicolon it should exit the program.

C++ Syntax (Toggle Plain Text)
  1. if input == ";"
  2.   Then exit
  3. end if

>i can't get the program to restart and ask the enter the expression thing.

So are you telling me you know how to write a infix to postfix program but don't understand the basic while loop?
Last edited by iamthwee; Nov 11th, 2006 at 4:53 am.
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This thread is more than three months old

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