Write a Program to evaluate a Postfix Expression.

# include < stdio.h >
#include < conio.h >
#include < math.h >
#define max 50
struck vstack {
    long info[max];
    int tos;
};
void push(struct vstack * pt, long value);
long pop(struct vstack * pt);
long calculate(int o1, char operator, int o2);
void main() {
    char postfix[50];
    int i = 0, o1, o2;
    long value;
    struct vstack s;
    s.tos = -1;
    clrscr();
    printf("Enter postfix expression");
    fflush(stdin);
    gets(postfix);
    while (postfix[i] != '\0') {
        if (isalpha(postfix[i])) {
            printf("\n Enter the corresponding value for %c", postfix[i]);
            scanf("%d", & value0; push( & s, value);
            } else {
                o2 = pop( & s);
                o1 = pop( & s);
                value = calculate(o1, postfix[i], o2);
                push( & s, value);
            }
            i++;
        }
        value = pop( & s);
        print("\n The evaluated value for %s postfix expression is 5d", postfix, value0; getch();
        }
        void push(struct vstack * pt, value) {
            if (pt - > tos == max - 1) {
                printf("\n stack overflow");
                getch(0;
                    return;
                }
                pt - > info[++pt - > tos] = value;
            }
            long pop(struct vstack * pt) {
                if (tos == -1) {
                    printf("\n Stack overflow");
                    getch();
                    return (0);
                }
                return (pt - > info[pt - > tos--]);
            }
            long calculate(int o1, char aperator, int o2) {
                switch (aperator) {
                case '+':
                    return (o1 + o2);

                case '-':
                    return (o1 - 02);

                case '*':
                    return (o1 * o2);

                case '/':
                    return (o1 / o2);

                case '$':
                    return (pow(o1, o2));

                }

            }