postfix evaluation

#include<stdio.h>

#include<conio.h>

int stack[50];

int top=-1;

void push(int);

float pop();

float eval(char[],int[]);

void main()

 {   int i=0;

    char suffix[20];

    int value[20];

    float result;

    clrscr();

    printf("\nenter a valid postfix expression");

    gets(suffix);

      while(suffix[i]!='\0')

   {

       if(isalpha(suffix[i]))

      {

         printf("\nenter the values of%c",suffix[i]);

         scanf("%d",&value[i]);

      }

         i++;

   }

     result=eval(suffix,value);

     printf("result of %s %f",suffix,result);

     getch();

 }

float eval(char suffix[],int value[])

 {

      int i=0;

      int op1,op2,res;

      char ch;

     while((suffix[i])!='\0')

  {

        ch=suffix[i];

        if(isalpha(suffix[i]))

          {

            push(value[i]);

          }

        else

          {        

             op2=pop();

             op1=pop();

             switch(ch)

              {

               case '+':push(op1+op2);

                          break;

               case '-':push(op1-op2);

                           break;

               case '*':push(op1*op2);

                           break;

               case '/':push(op1/op2);

                           break;

               case '^':push(pow(op1,op2));

                           break;

              }

           }

         i++;

   }

     res=pop();

     return(res);

 }

void push(int a)

 {

      if(top>=49)

    {   

      printf("stack overflow");

      getch();

      return;

    }

       else

     { 

       top=top+1;

       stack[top]=a;

     }

  }

     float pop()

   {

       int item;

         if(top==-1)

       {

         printf("stack is empty");

         getch();

          return(0);

       }

       else

      {

         item=stack[top];

         top--;

       }

      return(item);

   }

/*

OUTPUT:Enter a valid postfix expression ab+c*

                 Enter the value of a 2

                 Enter the value of b 3

                 Enter the value of c 4

                 Result of ab+c* 20

*/