evaluate postfix expression

/* This program is for evaluation of postfix expression
 * This program assume that there are only four operators
 * (*, /, +, -) in an expression and operand is single digit only
 * Further this program does not do any error handling e.g.
 * it does not check that entered postfix expression is valid
 * or not.
 * */

 #include<stdio.h>
 #include<ctype.h>


 # define MAXSTACK 100        /* for max size of stack */
 # define POSTFIXSIZE 100     /* define max number of charcters in postfix expression */

 /* declare stack and its top pointer to be used during postfix expression
    evaluation*/
 int stack[MAXSTACK];
 int top = -1 ;             /* because array index in C begins at 0 */
 /* can be do this initialization somewhere else */

 /* define push operation */
 void push(int item)
 {

     if(top >= MAXSTACK -1)
     {
         printf("stack over flow");
         return;
     }
     else
     {
         top = top + 1 ;
         stack[top]= item;
     }
 }

 /* define pop operation */
 int pop()
 {
     int item;
     if(top <0)
     {
        printf("stack under flow");
     }
     else
     {
         item = stack[top];
         top = top - 1;
         return item;
     }
 }

 /* define function that is used to input postfix expression and to evaluate it */
 void EvalPostfix(char postfix[])
 {

    int i ;
    char ch;
    int val;
    int A, B ;


    /* evaluate postfix expression */
    for (i = 0 ; postfix[i] != ')'; i++)
    {
        ch = postfix[i];
        if (isdigit(ch))
        {
            /* we saw an operand,push the digit onto stack
            ch - '0' is used for getting digit rather than ASCII code of digit */
            push(ch - '0');
        }
        else if (ch == '+' || ch == '-' || ch == '*' || ch == '/')
        {
            /* we saw an operator
            * pop top element A and next-to-top elemnet B
            * from stack and compute B operator A
            */
            A = pop();
            B = pop();

            switch (ch) /* ch is an operator */
            {
                case '*':
                val = B * A;
                break;

                case '/':
                val = B / A;
                break;

                case '+':
                val = B + A;
                break;

                case '-':
                val = B - A;
                break;
            }

            /* push the value obtained above onto the stack */
            push(val);
        }
    }
    printf( " \n Result of expression evaluation : %d \n", pop()) ;
 }

 int main()
 {

    int i ;

    /* declare character array to store postfix expression */
    char postfix[POSTFIXSIZE];
    printf("ASSUMPTION: There are only four operators(*, /, +, -) in an expression and operand is single digit only.\n");
    printf( " \nEnter postfix expression,\npress right parenthesis ')' for end expression : ");

    /* take input of postfix expression from user */

    for (i = 0 ; i <= POSTFIXSIZE - 1 ; i++)
    {
        scanf("%c", &postfix[i]);

        if ( postfix[i] == ')' ) /* is there any way to eliminate this if */
        { break; } /* and break statement */
    }

    /* call function to evaluate postfix expression */

    EvalPostfix(postfix);

    return 0;
 }