PE14_10.obj : error LNK2019: 无法解析的外部符号 "int __cdecl menu(void)" (?menu@@YAHXZ)，该符号在函数 _main 中被引用

#include <stdio.h>
#include <string.h>
#include <ctype.h>

float add(float x, float y);
float subtract(float x, float y);
float multiply(float x, float y);
float divide(float x, float y);
int menu(void);
int getlet(char *);

int main(void)
{
    float(*pf)(float x, float y); //函数指针
    int choice;
    float x, y;

    while ((choice = menu()) != 'e')
    {
        switch (choice)
        {
        case 'a': pf = add; break;
        case 'b': pf = subtract; break;
        case 'c': pf = multiply; break;
        case 'd': pf = divide; break;
        }
        printf("Please enret x y:");
        while (scanf("%f%f", &x, &y) !=2)
            printf("Error! Please enret x y:");
        printf("%.2f\n", pf(x,y));
    }

    
    return 0;
}

int meun(void)
{    
    puts("Enter menu choice:");
    puts("a) +");
    puts("b) -");
    puts("c) *");
    puts("d) /");
    puts("e) Quit");
    return getlet("abcde");
}
int getlet(char * str)
{
    char c;
    c = tolower(getchar());
    while (strchr(str, c) == NULL)
    {
        printf("Please enter (%s)\n", str);
        while (getchar() != '\n');
        c = tolower(getchar());
    }
    while (getchar() !='\n');

    return c;
}
float add(float x, float y)
{
    return (x + y);
}
float subtract(float x, float y)
{
    return (x - y);
}
float multiply(float x, float y)
{
    return (x * y);
}
float divide(float x, float y)
{
    return (x / y);
}

不是，本来是做课后关函数指针的习题。编译不通过就改成这样了

找了好久，硬是没看出来。下次实找不到就把相关标识全部换一遍。

拼音比英文更差，英文是初中水平而且考试从来不及格。拼音到现在也分不清声母，韵母。