Building a CLI Menu

One of the most common tasks in systems programming is building an interactive Command Line Interface (CLI) menu. However, doing this in standard C often introduces a severe bug: the infinite input loop.

If you build a menu using a standard while loop and ask for the user’s choice using scanf("%d", &choice), your program expects an integer. If the user accidentally types a letter (like “A”), scanf fails to read it, but it leaves the letter in the input buffer. The loop repeats, scanf sees the same letter, fails again, and your terminal is instantly flooded with an infinite loop of repeated prompts.

NextStd completely eliminates this class of bugs.

The NextStd Approach

By combining ns_read, our ns_color macros, and NS_TRY/NS_EXCEPT blocks, you can build a menu that is completely bulletproof.

When you use ns_read(&op), the Rust backend safely reads the input line. If the user types “A” instead of a number, it catches the parsing error, flushes the bad input, and cleanly throws an NS_ERROR_INVALID_INPUT error. Your program can catch it, print a polite warning, and safely wait for the next input.

The Complete Example

Here is a fully functional “System Control” menu. Try running this and intentionally typing words instead of numbers—notice how it handles the errors gracefully without ever crashing or looping infinitely!

#include <nextstd/ns.h>
#include <nextstd/ns_color.h>
#include <stdbool.h>

int main(void)
{
  int op = 0;     // Option
  ns_error_t err;
  bool continue_loop = true;

  while (continue_loop) {
    ns_println("Choose any of the below options: ");
    ns_println("1. First Option\n2. Second Option \n3. Third Option \n4. Exit");
    ns_print("Enter your option: ");
    NS_TRY(err, ns_read(&op)) {
      if (op == 1) {
        ns_println(NS_COLOR_GREEN "You chose option 1" NS_COLOR_RESET);
      }
      else if (op == 2) {
        ns_println(NS_COLOR_BLUE "You chose option 2" NS_COLOR_RESET);
      } else if (op == 3) {
        ns_println(NS_COLOR_MAGENTA "You chose option 3" NS_COLOR_RESET);
      } else {
        ns_println(NS_COLOR_YELLOW "Exiting...." NS_COLOR_RESET);
        continue_loop = false;
      }
    }
    NS_EXCEPT(err, NS_ERROR_INVALID_INPUT) {
      ns_println(NS_COLOR_RED "Wrong input" NS_COLOR_RESET);
      ns_println(ns_error_message(err));
    }
  }
}

Why this works so well

• State Management: The continue_loop boolean gives us a clean way to break out of the infinite while loop when the user selects the Exit option.
• Aesthetic Feedback: The ns_color macros provide instant visual feedback. Successes are green, information is blue/magenta, warnings are yellow, and errors are red.
• Absolute Stability: The NS_TRY block isolates the unpredictable nature of human input, guaranteeing the program state remains valid.