警告：隐式声明

我有一项计算机科学 MOOC CS50 作业需要交。在其中，我必须通过哈佛网站提交作业，但它不会接受我的代码，因为它显示“警告：隐式声明......”

有办法关闭它吗？

我正在使用两个函数，islower(), and isupper()，它们就是导致挂断的原因。

我的代码似乎工作得很好，它可以编译等等。顺便说一句，如果有人想告诉我我的代码有多糟糕，我将不胜感激。我通过网络上课并没有受到很多（或任何）批评。

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

int main(int argc, string argv[])
{
    int salt, cipherNum;
    char cipher[40];
    char letter;


    //// Greeting
    printf("Please enter the text to ceez...\n");
    //// grab text

    string txxt = GetString();


    if (argc == 2) // must have command line argument
    {

        salt = atoi(argv[1]) % 26;
        //printf("Salt: %d\n", salt);
    }

    else // yell at user if command line arg is not there
    {
        printf("Not cool! I need something to caesariphy...\n");
        return 1;
    }

    //~ 
    // This will iterate over each letter in the text
    for (int i = 0, n = strlen(txxt); i < n; i++)
    {
        // int letter = 'A'; i.e. 65 
        // Must Preserve Case

        //~ printf("%c---\n", txxt[i]);

        //if lower start from 'a'or 97
        if ( islower(txxt[i]) )
        {
            //~ printf("islower\n");
            letter = txxt[i];
            cipherNum = txxt[i];
            //~ printf("%c is the letter\n", letter + salt);
            //~ printf("%d is the cipherNumz\n", cipherNum);

            if ((letter + salt) > 122)
            { 
                //~ printf("letter + salt is > 90: %d \n", letter+salt);
                cipherNum = (96 + (cipherNum + salt) % 122);
                //~ printf("%c is the letters", cipherNum); 
            }
            else
            {
                cipherNum = letter + salt;
            }



            cipher[i] = cipherNum ;

        }
        else if ( isupper(txxt[i]))
        {

            letter = txxt[i];
            cipherNum = txxt[i];
            //printf("%c is the letter\n", letter + salt);
            //printf("%d is the cipherNumz\n", cipherNum);

            if ((letter + salt) > 90)
            { 
                //printf("letter + salt is > 90: %d \n", letter+salt);
                cipherNum = (64 + (cipherNum + salt) % 90);
                //printf("%c is the letters", cipherNum); 
            }
            else
            {
                cipherNum = letter + salt;
            }

            //printf("%c\n", cipherNum);
            cipher[i] = cipherNum ;
            //printf("testing12\n");    
        }
        else
        {
            cipher[i] = txxt[i];
        }
        //~ 

    }
    cipher[strlen(txxt) + 1] = '\0';
    printf("%s\n", cipher);


    return 0;
}

如果您使用的是标准islower and isalpha，然后在顶部的某个地方你应该看到

#include <ctype.h>

为了实现这一点。