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infix to postfix

Discussion in 'C++' started by vg_2007, Oct 15, 2008.

  1. vg_2007

    vg_2007 New Member

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    cn some bdy check my program i am getting a small error in it




    Code:
    #include<stdio.h>
    #include<conio.h>
    #include <iostream.h>
    #include <stdlib.h>
    #include <string.h>
    const int size=50;
    char infix[size],postfix[size],stack[size];
    int top=-1;
    
    int precedence(char ch);
    char pop();
    char topelement();
    void push(char ch);
    int braces(char *);
    
    void main()
    {
     char ele,elem,st[2];
     int prep,pre,popped,j=0,chk=0;
     strcpy(postfix," ");
     clrscr();
     cout<<"ASSUMPTION: the inflix expression contains single letter variables \n\t"<<"\t and single digit constants only \n\n";
     cout<<"\n ENTER INFIX EXPRESSION ....\n" ;
     gets(infix);
     chk=braces(infix);
     if(chk!=0)
     {
     cout<<"UNBALANCED NO. OF BRACES  \n EXTRA ";
     cout<< (chk==1?"right braces ":"left braces ")<<endl;
     getch();
     exit(1);
     }
     for(int i=0;infix[i]!=	NULL;i++)
     {
     if(infix[i]!='('&&infix[i]!=')'&& infix[i]!='^'&& infix[i]!='*' && infix[i]!='/'&& infix[i]!='+'&& infix[i]!='-')
     {
     postfix[j++]=infix[i];
     }
     else if (infix[i]=='(')
     {
     elem=infix[i];
     push(elem);
     }
     else if(infix[i]==')')
     {
     while((popped=pop())!='(')
    	{
    	postfix[j++]=popped;
    	 }
     }
    else
    {
    elem=infix[i];
    pre=precedence(elem);
    ele=topelement();
    prep=precedence(ele);
    if(pre>prep)
    push(elem);
    else
    {
    while(prep>=pre)
    {
    if(ele=='#')
    break;
    popped=pop();
    ele=topelement();
    postfix[j++]=popped;
    prep=precedence(ele);
    }
    push(elem);
    }
    }
    }
    while((popped=pop())!='#')
    postfix[j++]=popped;
    postfix[j]='\0';
    cout<<"\n POSTFIX: "<<postfix<<endl;
    }
    
    
    int precedence(char ch)
    {
    switch (ch)
    	{
    	 case '^':return 5;
    	 case '/':return 4;
    	 case '*':return 4;
    	 case '+':return 3;
    	 case '-':return 3;
    	 default :return 4;
    	 }
    	 }
    
    char pop()
    {
    char ret;
    if(top!=-1)
    {
    ret=stack[top];
    top--;
    return ret;
    }
    else
    return'#';
    }
    
    char topelement()
    {
     char ch;
     if(top!=-1)
     ch=stack[top];
     else ch='#';
     return ch;
     }
    
     void push(char ch)
     {
     if(top!=size-1)
     {
     top++;
     stack[top]=ch;
     }
     }
    
     int braces(char *s)
     {
     int leftbr,rightbr;
     leftbr=rightbr=0;
     for(int i=0;s[i];i++)
     {
     if(s[i]=='(');
     leftbr++;
     if(s[i]==')')
     rightbr++;
     }
     if(leftbr==rightbr)
     return 0;
     else
     if (leftbr<rightbr)
     return 1;
     else
     return -1;
     }
     
    Last edited by a moderator: Oct 16, 2008
  2. oogabooga

    oogabooga New Member

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    Please do two things:
    1. Put your code in code blocks so that the indentation is preserved.
    2. Be more specific about the error.
    Same thing with your other post.
     
  3. shabbir

    shabbir Administrator Staff Member

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    As already pointed out by oogabooga, Let us know the error and not all of your code with where is the error to find.
     

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