program for covert infix to postfix

#include<stdio.h>

#include<conio.h>

#include<stdlib.h>

struct stack

{

      char s[30];

      int top;

}st;

main()

{

      char infix[30],postfix[30];

      void intopost(char infix[30]);

      printf("Enter expression=");

      gets(infix);

      intopost(infix);

      //printf("\n\nThe postfix expression is=");

      //puts(postfix);

      getch();

}

void intopost(char infix[30])

{

      int i,j;

      char postfix[30];

      char ch;

      int incoming(char ch);

      int instack(char ch);

      void push(char item);

      char pop();

      st.top=-1;

      st.top=st.top++;

      st.s[st.top]='$';

      j=0;

      for(i=0;infix[i]!='\0';i++)

      {

            ch=infix[i];

            while(instack(st.s[st.top])>incoming(ch))

            {

                  postfix[j]=pop();

                  j++;

            }

            if(instack(st.s[st.top])!=incoming(ch))

            push(ch);

            else

            pop();

      }

      while(ch=pop()!='$')

      {

            postfix[j]=ch;

            j++;

      }

      postfix[i]='\0';

      printf("\n\nThe postfix expression is=%s",postfix);

}

int instack(char ch)

{

      int priority;

      switch(ch)

      {

            case '+':

            case '-':

            priority=2;

            break;

      case '*':

            case '/':

            priority=4;

            break;

            case '^':

            priority=5;

            break;

            case '(':

            priority=0;

            break;

            case '$':

            priority=-1;

            break;

      default:

            priority=8;

      }

      return(priority);

}

int incoming(char ch)

{

      int priority;

      switch(ch)

      {

            case '+':

            case '-':

            priority=1;

            break;

      case '*':

            case '/':

            priority=3;

            break;

            case '^':

            priority=6;

            break;

            case '(':

            priority=9;

            break;

            case '$':

            priority=0;

            break;

      default:

            priority=7;

      }

      return(priority);

}

void push(char item)

{

      st.top++;

      st.s[st.top]=item;

}

char pop()

{

      char e;

      e=st.s[st.top];

      st.top--;

      return e;

}