calculator.c

#include <stdio.h>

int main(void) {
    int choice;
    double num1, num2;

    while (1) {
        printf("\n===== Basic Calculator =====\n");
        printf("1. Addition (+)\n");
        printf("2. Subtraction (-)\n");
        printf("3. Multiplication (*)\n");
        printf("4. Division (/)\n");
        printf("5. Exit\n");
        printf("Enter your choice (1-5): ");

        if (scanf("%d", &choice) != 1) {
            // clear invalid input from stdin
            int c;
            while ((c = getchar()) != '\n' && c != EOF) { }
            printf("Invalid choice. Please enter a number between 1 and 5.\n");
            continue;
        }

        if (choice == 5) {
            printf("Goodbye!\n");
            break;
        }

        printf("Enter two numbers separated by space: ");
        if (scanf("%lf %lf", &num1, &num2) != 2) {
            int c;
            while ((c = getchar()) != '\n' && c != EOF) { }
            printf("Invalid numbers. Try again.\n");
            continue;
        }

        switch (choice) {
            case 1:
                printf("%.6f + %.6f = %.6f\n", num1, num2, num1 + num2);
                break;
            case 2:
                printf("%.6f - %.6f = %.6f\n", num1, num2, num1 - num2);
                break;
            case 3:
                printf("%.6f * %.6f = %.6f\n", num1, num2, num1 * num2);
                break;
            case 4:
                if (num2 == 0.0) {
                    printf("Error: Division by zero is not allowed.\n");
                } else {
                    printf("%.6f / %.6f = %.6f\n", num1, num2, num1 / num2);
                }
                break;
            default:
                printf("Invalid choice. Please select between 1 and 5.\n");
                break;
        }
    }

    return 0;
}