Evaluation of Postfix Expression

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

 # define MAXSTACK 100
 # define POSTFIXSIZE 100

 int stack[MAXSTACK];
 int top = -1 ;

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

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

 void EvalPostfix(char postfix[])
 {
    int i ;
    char ch;
    int val;
    int A, B ;

    for (i = 0 ; postfix[i] != ')'; i++){

        ch = postfix[i];
        if (isdigit(ch))
        {
            push(ch - '0');
        }
        else if (ch == '+' || ch == '-' || ch == '*' || ch == '/'){
            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(val);
        }
    }
    printf( " \n Result of expression evaluation : %d \n", pop()) ;
 }

 int main()
 {
    int i ;
    char postfix[POSTFIXSIZE];

    for (i = 0 ; i <= POSTFIXSIZE - 1 ; i++){

        scanf("%c", &postfix[i]);

        if ( postfix[i] == ')' )
        { break; }
    }
    EvalPostfix(postfix);

    return 0;
 }