防止读取和返回字符串值

Question

int getIndex(){
    int index = 0;
    do{
        printf("Enter your Index(0..80),-1 to STOP,-2 to RESTART,-3 to START NEW BOARD: ");
        scanf("%d", &index);
    } while (!(index >= -3 && index <=80));

    return index;

}

您好，鉴于我已经用 C 语言为数独游戏板编写了上述方法。我能做些什么来防止用户输入字母？并一直提示直到得到有效的输入。我刚刚开始 C 。限制我的是 scanf 标志说明符，我指定了一个 int 标志，这意味着如果用户输入一个字符串，我就搞砸了。

Answer 1

您只需检查scanf 的返回值，然后在输入任何无效输入时从输入缓冲区(stdin) 中清除该字符。因此，将您的代码更改为以下内容：

int getIndex()
{
    int index = 0;

    while(1) //infinite loop
    {    printf("Enter your Index(0..80),-1 to STOP,-2 to RESTART,-3 to START NEW BOARD: ");
        if(scanf("%d", &index)==1) //scanf is successful scanning a number(input is a number)
        {
          if(index >= -3 && index <= 80) // if input is in range
          break; //break out of while loop
          printf("Number must be in range of -3 to 80\n"); //input is a number,but not in range
        }
        else  //input is not a number
        {
        scanf("%*s"); //Clear invalid input
        //printf("Invalid input\n");
        fprintf(stderr, "Invalid input\n"); //printf also works but errors are meant to be in the stderr
        }

    }

    return index;
}