控制可能到达非 void 函数的末尾。频率

Question

我不知道为什么这个程序无法编译。它告诉我有一个问题，但我只是不知道这段代码有什么问题。

我正在在线学习哈佛的 CS50 入门类(class)，但在编写此函数频率时遇到困难。我知道这可以更简单地编码，但我只是还没有经验让编程变得更加流畅和优雅。问题似乎出现在函数的最后。我猜我忘记返回一个值，但我不知道发生了什么。

//Calculates frequency (in Hz) of a note

#include <cs50.h>
#include <string.h>
#include <math.h>
#include <stdio.h>

int frequency(string note);

int main(void)
{
string note = get_string();
printf("Piano Note: ");
frequency(note);
return 0;
}

int frequency(string note)
{
char key = note[0];
char accidental;
int octave;

int counter = 0;

while (note != '\0')
{
    counter++;
}

if(counter == 3)
    accidental = note[1];
    octave = note[2];
if(counter == 2)
    octave = note[1];

if (counter == 3)
{
    if (key == 'A')
    {
        if (accidental == '#')
        {
                if(octave == 4)
                {
                    return 466;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }
        }

        else if (accidental == 'b')
        {
            if(octave == 4)
                {
                    return 415;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }
        }
    }

    else if (key == 'B')
    {
        if (accidental == '#')
        {
            if(octave == 4)
                {
                    return 523;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
        }

        else if (accidental == 'b')
        {
            if(octave == 4)
                {
                    return 466;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
        }
    }

    else if (key == 'C')
    {
        if (accidental == '#')
        {
             if(octave == 4)
                {
                    return 277;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)8/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if (octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)8/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }

        else if (accidental == 'b')
        {
             if(octave == 4)
                {
                    return 247;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)10/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if (octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)10/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }
    }

    else if (key == 'D')
    {
        if (accidental == '#')
        {
            if(octave == 4)
                {
                    return 311;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)6/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)6/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }

        else if (accidental == 'b')
        {
            if(octave == 4)
                {
                    return 277;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)8/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)8/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }
    }

    else if (key == 'E')
    {
        if (accidental == '#')
        {
            if(octave == 4)
                {
                    return 349;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)4/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)4/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }

        else if (accidental == 'b')
        {
            if(octave == 4)
                {
                    return 311;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)6/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)6/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }
    }

    else if (key == 'F')
    {
        if (accidental == '#')
        {
             if(octave == 4)
                {
                    return 370;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }}

        else if (accidental == 'b')
        {
             if(octave == 4)
                {
                    return 330;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)5/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)5/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }
    }

    else if (key == 'G')
    {
        if (accidental == '#')
        {
             if(octave == 4)
                {
                    return 415;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)1/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }

        else if (accidental == 'b')
        {
             if(octave == 4)
                {
                    return 370;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
        }
    }
}

    if (counter == 2)
    {
            if(key == 'A')
            {

                if(octave == 4)
                {
                    return 440;
                }

                else if(octave < 4)
                {
                    int count = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int divisor = 0, hertz = 440;
                    while(divisor != count)
                    {
                        hertz /= 2;
                        divisor++;
                    }
                    return hertz;
                }

                else if(octave > 4)
                {
                    int count = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int divisor = 0, hertz = 440;
                    while(divisor != count)
                    {
                        hertz *= 2;
                        divisor++;
                    }
                    return hertz;
                }
            }

            else if(key == 'B')
            {

                if(octave == 4)
                {
                    return 494;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)2/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 * pow((double)2, (double)2/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }
            }


            else if(key == 'C')
            {
                if(octave == 4)
                {
                    return 262;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)9/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if (octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)9/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }
            }

            else if(key == 'D')
            {
                if(octave == 4)
                {
                    return 294;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)7/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)7/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }
            }

            else if(key == 'E')
            {
                if(octave == 4)
                {
                    return 330;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)5/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)5/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }
            }

            else if(key == 'F')
            {
                if(octave == 4)
                {
                    return 349;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)3/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }
            }

            else if(key == 'G')
            {
                if(octave == 4)
                {
                    return 392;
                }

                else if(octave > 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i < octave; i++)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)2/12));
                    while(shade != count)
                    {
                        answer *= 2;
                        shade++;
                    }
                    return answer;
                }

                else if(octave < 4)
                {
                    int count = 0, shade = 0;
                    for(int i = 4; i > octave; i--)
                    {
                        count++;
                    }
                    int answer = (440 / pow((double)2, (double)2/12));
                    while(shade != count)
                    {
                        answer /= 2;
                        shade++;
                    }
                    return answer;
                }

            }
    }
}}}}}}}}}}}}

Answer 1

虽然该代码看起来很难读，但编译错误表明您的函数有一个分支将在没有 return 语句的情况下到达函数末尾。如果看起来可行，请在函数中添加默认返回值，例如 int retVal = 0;然后在函数结束之前放置一行 return retVal;

我没有阅读您的整个示例源代码。您可能有 if/elseif/elseif/etc 没有 else 情况，它也应该返回默认值，这将通过该编译类型错误。

如果您不想返回默认值，请返回错误代码并让调用者检查它以确保其执行您认为其执行的操作。

编辑，例如，如果 counter == 1，您的函数将不会返回任何内容。这是编译器试图告诉您的一个例子，可能还有更多。