#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;
};

// Function declarations
void push_stack(struct stack* stack, float value);
float pop_stack(struct stack* stack);
void print_stack(struct stack* stack);
int is_number(const char* str);

int main() {
    struct stack mystack;
    memset(&mystack, 0, sizeof(struct stack)); // Initialize the stack

    char input[50];
    while (1) {
        printf("Enter a number or an operator (+, -, *, /): ");
        if (!fgets(input, sizeof(input), stdin)) {
            break; // Exit on EOF
        }
        // Remove trailing newline character
        input[strcspn(input, "\n")] = 0;

        // Check if the input is empty
        if (strlen(input) == 0) {
            printf("no input\n");
            break;
        }

        if (is_number(input)) {
            // Convert input to float and push onto stack
            float value = atof(input);
            push_stack(&mystack, value);
        } else if (strlen(input) == 1 && strchr("+-*/", input[0])) {
            // Perform operation
            if (mystack.size < 2) {
                fprintf(stderr, "Error: Not enough values in stack.\n");
                exit(EXIT_FAILURE);
            }
            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) {
                        fprintf(stderr, "Error: Division by zero.\n");
                        exit(EXIT_FAILURE);
                    }
                    result = a / b;
                    break;
                default:
                    fprintf(stderr, "Error: Invalid operator.\n");
                    exit(EXIT_FAILURE);
            }
            push_stack(&mystack, result);
        } else {
            fprintf(stderr, "Error: Invalid input.\n");
            exit(EXIT_FAILURE);
        }

        // Print the current stack
        print_stack(&mystack);
    }

    return 0;
}

// Push a value onto the stack
void push_stack(struct stack* stack, float value) {
    assert(stack->size < STACK_SIZE); // Ensure there's space in the stack
    stack->values[stack->size] = value;
    stack->size += 1;
}

// Pop a value from the stack
float pop_stack(struct stack* stack) {
    assert(stack->size > 0); // Ensure there's something to pop
    stack->size -= 1;
    return stack->values[stack->size];
}

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

// Check if the input string is a valid number
int is_number(const char* str) {
    char* endptr;
    strtod(str, &endptr);
    return *endptr == '\0' && endptr != str;
}