当我输入 "sine"时，C 计算器程序一直出错？

Question

大家好，我是编程新手，现在已经在计算器上工作了一段时间。我正在尝试添加一些三角函数，但我在使用正弦函数时遇到了问题。其他函数有效(+、-、*、/)，但是当我输入“正弦”时，它会跳到代码中表示它是错误函数的部分。请帮助我的代码。谢谢!

#include <stdio.h>
#include <math.h>


int main() 
{

    float firstnum, secondnum, angle, answer, pi;
    char function, sine;


    pi = atan(1.0)*4;


    printf("\nHello and welcome to my calculator!\n");

    while(1) 
    {      

        printf("\nPlease input the function you would like to use.  These include +, -, *, /, sine.\n");     
        scanf("%s", &function);   



        switch(function)
        {
            case '+': 
            printf("\nNow please input the two variables.\n");  
            scanf("%f", &firstnum);
            scanf("%f", &secondnum);
            answer = firstnum+secondnum;
            break;

            case '-': 
            printf("\nNow please input the two variables.\n");  
            scanf("%f", &firstnum);
            scanf("%f", &secondnum);
            answer = firstnum-secondnum;
            break;

            case '*': 
            printf("\nNow please input the two variables.\n");  
            scanf("%f", &firstnum);
            scanf("%f", &secondnum);
            answer = firstnum*secondnum;
            break;

            case '/': 
            printf("\nNow please input the two variables.\n");  
            scanf("%f", &firstnum);
            scanf("%f", &secondnum);
            answer = firstnum/secondnum;
            break;

            case 'sine':
            printf("\nPlease enter the angle.\n");
            scanf("%f", &angle);
            answer = sin(angle);
            break;



            default: printf("Sorry, that is an incorrect function.  The only available choices are +, -, *, /, sine.");
            break;
        }   

        printf("Your answer is %f \n", answer);  
        printf("\nWhen you are ready to quit, simply press Ctrl + C or just hit the X button in the top right.\n");
    } 

     return 0;
}

Answer 1

'sine'

这是一个多字 rune 字。 function 是单个字符。它的整数值在 switch 语句中检查。您可能永远无法以您尝试这样做的方式使用与 sine 匹配的用户的单个字符。改为读取字符串 (a char*)。

来自标准:

C99 6.4.4.4p10: "The value of an integer character constant containing more than one character (e.g., 'ab'), or containing a character or escape sequence that does not map to a single-byte execution character, is implementation-defined."