C 中 do while 循环条件错误

Question

我在尝试这部分程序时在 Xcode 中收到 "code will never be executed" 警告。警告出现在 do while 循环的 while 部分的条件中。如果未输入列表中显示的数字之一，则应该打印以下字符串。有什么建议吗？

#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 条件只需要一个条件就可以计算为真，因此如果用户输入为 1

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

以此类推

使用 && 运算符这将检查如果您的输入不是 1,2,3,4 它会中断

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;

}

虽然不是 1 也不是 2 也不是 3 也不是 4 它将再次重复

C 中 do while 循环条件错误

error on do while loop condition in C

c

loops

conditional-statements

do-while