program to covert prefix to postfix

#include<stdio.h>

#include<conio.h>

#include<ctype.h>

#define MAX 30

char stack[MAX][MAX];

int top;

void pre_to_post(char prefix[],char postfix[]);

void convert_postfix(char x);

main()

{

      char prefix[30],postfix[30];

      printf("Enter prefix=");

      gets(prefix);

      pre_to_post(prefix,postfix);

      printf("The postfix expression is=");

      puts(postfix);

      getch();

}

void pre_to_post(char prefix[30],char postfix[30])

{

      int top=-1,i,n;

      char x,st1[30];

      n=strlen(prefix);

      for(i=n-1;i>=0;i--)

      {

            x=prefix[i];

            if(isalnum(x))

            {

                  st1[0]=x;

                  st1[1]='\0';

                  top++;

                  strcpy(stack[top],st1);

            }

            else

            {

                  convert_postfix(x);

            }

      }

      strcpy(postfix,stack[top]);

}

void convert_postfix(char x)

{

      char st1[30],st2[30];

      st2[0]=x;

                  st2[1]='\0';

                  strcpy(st1,stack[top]);

                  strcat(st1,stack[top-1]);

                  strcat(st1,st2);

                  top=top-1;

                  strcpy(stack[top],st1);

}