Example program (user_menu_code.c) for presenting a text menu to the user and getting a valid option from the user.

[Amit]

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user_menu_code.c
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/*
 * License: This file has been released under GNU General Public License,
 *          version 2 (GPLv2).
 *
 * The license details can be found here:
 *                  https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

#define NUM_TRUE  1
#define NUM_FALSE 0

// function prototypes for gcc flag -Werror-implicit-function-declaration
char *get_input_from_stdin_and_discard_extra_characters(char *str, long size);
int is_str_a_number(const char *str);
void print_menu(void);
int print_menu_and_get_valid_user_option(void);
void process_user_option(int option);
void __func(int option);

char *get_input_from_stdin_and_discard_extra_characters(char *str, long size)
{

    int c = 0;
    long i = 0;

    // If 'size' is 0 then this function will discard all input and return NULL.
    // No need to check 'str' if 'size' is 0.
    if (size == 0) {
        // discard all input
        while ((c = getchar()) && (c != '\n') && (c != EOF));
        return NULL;
    }

    if (str == NULL)
        return NULL;

    if (size < 0)
        return NULL;

    for (i = 0; i < (size - 1); i = i + 1) {

        c = getchar();

        if ((c == '\n') || (c == EOF)) {
            str[i] = 0;
            return str;
        }

        str[i] = (char)(c);

    } // end of for loop

    str[i] = 0;

    // discard rest of input
    while ((c = getchar()) && (c != '\n') && (c != EOF));

    return str;

} // end of function get_input_from_stdin_and_discard_extra_characters()

int is_str_a_number(const char *str)
{

    char c = '=';

    if (str == NULL) {
        return NUM_FALSE;
    }

    if (str[0] == '\0') { // empty string
        return NUM_FALSE;
    }

    while ((c = *str)) {
        if ((c < '0') || (c > '9')) {
            return NUM_FALSE;
        }
        str++;
    }

    return NUM_TRUE;

} // end of function is_str_a_number()

void print_menu(void)
{

    printf("\n\n");

    printf("----\n");
    printf("Menu\n");
    printf("----\n");
    printf("\n");

    printf("1. Option 1\n");
    printf("2. Option 2\n");
    printf("3. Option 3\n");
    printf("4. Exit\n");

    return;

} // end of function print_menu()

int print_menu_and_get_valid_user_option(void)
{
#define MIN_USER_OPTION 1
#define MAX_USER_OPTION 4
#define OPTION_SIZE     8

    char option_str[OPTION_SIZE] = {0};
    int option = -1;

    while (1) {

        print_menu();

        printf("\n");

        while (1) {

            printf("Please enter a valid option (%d - %d)"
                   " (spaces not allowed): ", MIN_USER_OPTION, MAX_USER_OPTION);

            get_input_from_stdin_and_discard_extra_characters(option_str,
                                                              OPTION_SIZE);

            if (is_str_a_number(option_str) != NUM_TRUE) {
                continue;
            }

            option = atoi(option_str);

            if ((option < MIN_USER_OPTION) || (option > MAX_USER_OPTION)) {
                continue;
            }

            printf("\n");
            printf("Option number given by the user is: %d\n", option);
            printf("\n");
            printf("Do you want to proceed (Enter only 'n' (without the quotes)"
                   " for not proceeding, enter any thing else for proceeding):"
                   " ");
            get_input_from_stdin_and_discard_extra_characters(option_str,
                                                              OPTION_SIZE);
            if (strcmp(option_str, "n") != 0) {
                return option;
            }

            break;

        } // end of inner while(1) loop

    }  // end of outer while(1) loop

    // Unreachable code. Program execution should not reach here.
    // Exit the program.
    printf("\n");
    printf("Line %d: Some BUG in the program. Exiting..\n", __LINE__);
    printf("\n");
    exit(1);

} // end of function print_menu_and_get_valid_user_option()

void process_user_option(int option)
{

    switch (option) {

        case 1: __func(option);
                break;
        case 2: __func(option);
                break;
        case 3: __func(option);
                break;
        case 4: printf("\n");
                printf("**THE USER GAVE OPTION NUMBER %d**\n", option);
                printf("\n");
                printf("Exiting..\n");
                printf("\n");
                exit(0);
        default: printf("\n");
                 printf("Line %d: Some BUG in the program. Exiting..\n",
                                                                    __LINE__);
                 printf("\n");
                 exit(1);

    } // end of switch statement

    return;

} // end of function process_user_option()

void __func(int option)
{

    printf("\n");
    printf("**THE USER GAVE OPTION NUMBER %d**\n", option);

    return;

} // end of function __func()

int main(void)
{
    int option = -1;

    while (1) {

        option = print_menu_and_get_valid_user_option();
        process_user_option(option);

    } // end of while loop

} // end of function main()