All in 1(one)

//Any quire then let me know// //help nd supported by shankhar koirala//
/*program to evaluate  postfix expression
AUTHER: Suman Thapa
DATE:013/07/02
TIME:1:11 AM*/
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define STACKSIZE 20


struct stack
{
    int top;
    double items[STACKSIZE];
};

double oper(int symbol, double x,double y);
int isDigit (char c);
double pop (struct stack *);
void push (struct stack *,double data);
double evaluate (char expr[]);




int main (void)
{


    char expression[16] =
{'6','2','3','+','-','3','8','2','/','+','*','2','$','3','+'};

    printf("\nthe given expression is : %s",expression);

    printf("\nthe evaluated value is : %f",evaluate(expression));

    getchar ();
    return 0;
}


double evaluate (char expr[])
{
    char c;
    int i;

    double operand1, operand2, value;
    struct stack s;
    s.top = -1;
    double num;

    for (i=0; (expr[i] )!=!'\0'; i++)
    {
         c=expr[i];
        if (isDigit(c) == 1)
        {
         
            num = c - 48;
           push(&s,num);
        }

        else
        {
            operand2 = pop(&s);
            operand1 = pop(&s);

            value = oper(c,operand1,operand2);

            push(&s,value);
        }

     
    }
    return (pop(&s));


}

void push (struct stack *s,double data)
{
        s->top++;
        s->items[s->top] = data;
}



double pop (struct stack *s)
{
    return (s->items[(s->top)--]);

}


int isDigit (char c)
{
    if (c >= '0' && c<= '9')
        return 1;
    else
        return 0;

}


double oper(int symbol, double x,double y)
{
    switch (symbol)
    {
        case '+' :
            return (x+y);

        case '-' :
            return (x-y);

        case '*' :
            return (x*y);

        case '/' :
            return (x/y);

        case '$' :
            return (pow(x,y));

    }


}