c - (c) 表达式必须是可修改的左值

Question

if (operation = '+' || operation = '-' || operation = '*' || operation = '/' || operation = '%')//error line
    {
        printf("Enter the first operand:\t\t");
        getchar();
        scanf("%d", &num1);
        printf("Enter the second operand:\t\t");
        getchar();
        scanf("%d", &num2);
}

它给出了一个错误说:

Error: expresion must be a modifiable value

它给了我关于那条 if 行的错误，关于所有的参数，除了那个说的那个

operation = '%'

问题是什么？？ 谢谢你们:)

Answer 1

你打错了，你写了赋值运算符 = 而不是比较运算符 ==

代替

if (operation = '+' || operation = '-' || operation = '*' || operation = '/' || operation = '%')

必须有

if (operation == '+' || operation == '-' || operation == '*' || operation == '/' || operation == '%')

您可以将 if 语句写得更简单。例如

const char *Operations = "+-*/%";

char *p = strchr( Operations, operation );

if ( p !=  NULL )
{
        printf("Enter the first operand:\t\t");
        getchar();
        scanf("%d", &num1);
        printf("Enter the second operand:\t\t");
        getchar();
        scanf("%d", &num2);
}

甚至不声明指针 p

const char *Operations = "+-*/%";

if ( strchr( Operations, operation ) !=  NULL )
{
        printf("Enter the first operand:\t\t");
        getchar();
        scanf("%d", &num1);
        printf("Enter the second operand:\t\t");
        getchar();
        scanf("%d", &num2);
}