/*Program for Transforming infix expression to postfix expression with Algorithm.
  Successfully Tested.*/
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int stack[20], TOP=-1;
void push(char e)
{
    stack[TOP++]=e;
}

int pop(){
    if(TOP==-1)
    return -1;
    else
    return stack[TOP--];
}

int highPrecedence(char operater)
{
    if(operater=='^')
    return 3;
    else if(operater=='*'||operater=='/')
    return 2;
    else if(operater=='+'||operater=='-')
    return 1;
    else
    return 0;
}

//Main fuunction execution starts here.
int main()
{
    char expression[20],x,*e;
    e=expression;
    printf("Enter Expression : ");
    scanf("%s",e); printf("%s",e);
/*Step1 : Push left parenthesis '(' on stack[TOP] and append right parenthesis at the end of expression. */
    push('(');
    strcat(e,")");
/*Step2 : Scan each element of an expression till null character not found. */
   while(*e!='\0'){
/*Step3 : If an operand is encountered the print it.*/
     if(isalnum(*e))
        printf("%c",*e);
     if(*e=='(')
        push(*e);
     if(*e==')'){
        while((x=pop())!='(')
        printf("%c",x); }
     else{
       while(highPrecedence(stack[TOP])>=highPrecedence(*e))
            printf("%c",pop());
           push(*e);
         }
       e++;
     }
}