C中的while循环条件中的错误

Question

I'm getting a "code will never be executed" warning in Xcode when trying out this part of the program. The warning appears in the condition for the while part of the do while loop. It is supposed to print the string below if one of the numbers shown in the list is not entered. Any suggestions?

#include <stdio.h>
#include <stdlib.h>
#include <time.h>


int main()
{

int input;

    do
    {
        printf("Welcome to the Arithmetic Quiz Program!\n\n
               Please choose one of the following by entering the correspoding number:\n\n
               1. Give me an addition problem.\n
               2. Give me a subtraction problem.\n
               3. Give me a multiplication problem.\n
               4. Quit.\n\n");

        scanf(" %i", &input);

    } while ( input!=1 || input!=2 || input!=3 || input!=4 );

return 0;

}

Answer 1

If your do while loop condition has all the conditions possible then it would never evaluate to false to break the loop

OR conditions need only one condition to evaluate to True so if user input is 1

Input!=1 //evaluates to false
Input!=2 //becomes True

And so on

Use && operator this would check that if your input is not 1,2,3,4 it would break

Answer 2

int main()
{

int input;

    do
    {
        printf("Welcome to the Arithmetic Quiz Program!\n\n
               Please choose one of the following by entering the correspoding number:\n\n
               1. Give me an addition problem.\n
               2. Give me a subtraction problem.\n
               3. Give me a multiplication problem.\n
               4. Quit.\n\n");

        scanf(" %i", &input);

    } while ( input!=1 && input!=2 && input!=3 && input!=4 );

return 0;

}

While are not 1 nor 2 nor 3 nor 4 it will repeat again