#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>

#define STACK_SIZE 10


struct stack {
    float values[STACK_SIZE];
    int size;
};


void init_stack(struct stack* s) {
    memset(s, 0, sizeof(struct stack));
}


void push_stack(struct stack* s, float value) {
    assert(s->size < STACK_SIZE); 
    s->values[s->size] = value;
    s->size += 1;
}


float pop_stack(struct stack* s) {
    assert(s->size > 0); 
    s->size -= 1;
    return s->values[s->size];
}


void print_stack(struct stack* s) {
    for (int i = 0; i < s->size; i++) {
        printf("%.2f ", s->values[i]);
    }
    printf("\n");
}


int is_number(const char* str) {
    char* endptr;
    strtof(str, &endptr);
    return endptr != str && *endptr == '\0'; 
}


int main() {
    struct stack mystack;
    init_stack(&mystack);

    char input[20]; 

    while (1) {
        printf("Enter a number or an operation (+, -, *, /): ");
        if (!fgets(input, sizeof(input), stdin)) {
            break; 
        }

        
        input[strcspn(input, "\n")] = 0;

        if (is_number(input)) {
            
            float value = strtof(input, NULL);
            push_stack(&mystack, value);
            print_stack(&mystack);
        } else {
            
            if (mystack.size < 2) {
                printf("Error: Not enough values on the stack to perform operation.\n");
                break; 
            }
            float b = pop_stack(&mystack);
            float a = pop_stack(&mystack);
            float result;

            switch (input[0]) {
                case '+':
                    result = a + b;
                    break;
                case '-':
                    result = a - b;
                    break;
                case '*':
                    result = a * b;
                    break;
                case '/':
                    if (b == 0) {
                        printf("Error: Division by zero.\n");
                        break;
                    }
                    result = a / b;
                    break;
                default:
                    printf("Error: Unknown operation '%s'.\n", input);
                    push_stack(&mystack, a); 
                    push_stack(&mystack, b);
                    break;
            }

            if (result) {
                push_stack(&mystack, result);
                print_stack(&mystack);
            }
        }
    }

    return 0;
}