Program to convert infix to postfix expression.

#include<stdio.h>

#include<conio.h>         

#include <ctype.h>

#define SIZE 50

char s[SIZE];

int top=-1;     

push(char c)

{                      

    s[++top]=c;

}

char pop()

{                      

    return(s[top--]);

}

int priority(char c)

{                

    switch(c){

    case '$':

      return 0;

    case '(':

      return 1;

    case '+':

    case '-':

      return 2;

    case '*':

    case '/':

      return 3;

    case '^':

      return 4;}

}

main()

{                        

char infix[50],postfix[50],ch,c;

    int i=0,j=0;

    printf("\nEnter the infix expression=\t");

    scanf("%s",infix);

    push('$');

    while((ch=infix[i++])!='\0')

    {

        if(ch =='(')

            push(ch);

        else if(isalnum(ch))

            postfix[j++]=ch;

            else if( ch ==')'){

            while(s[top] !='(')

                  postfix[j++]=pop();

                    c=pop();

                              }

        else{      

        while(priority(s[top])>=priority(ch))

        postfix[j++]=pop();

        push(ch);

        }

    }

    while( s[top] != '$')    

    postfix[j++]=pop();

    postfix[j]='\0';        

    printf("\n\nThe Postfix Expn: %s\n",postfix);

    getch();

}