凯撒 : lowercase letters that loop from z are not printing

Question

我有点被这个问题困住了。当我运行程序时，由于某种原因，循环经过 z 的所有字母都不会打印。问题来自这个链接:http://docs.cs50.net/2016/x/ap/problems/caesar/caesar.html这是我的代码:

#include <stdio.h>
#include <stdlib.h>
#include <cs50.h>
#include <ctype.h>
#include <string.h>

int main(int argc, string argv[])
{
    if (argv[1] != NULL)
    {
        int k = atoi(argv[1]);
        if ((argc == 2) && (k >= 0))
        {
            printf("Type what you would like to encrypt!\n");  
            string text = GetString();
            for (int i = 0, n = strlen(text); i < n; i++)
            {
                if (isalpha(text[i]) || isspace(text[i]))
                {
                    if (isupper(text[i]))
                    {
                        text[i] = text[i] + k;
                        if (text[i] > 'Z')
                        {
                            text[i] = text[i] - 26;
                            printf("%c", text[i]);
                        }
                        else
                        printf("%c", text[i]);
                    }
                    else if (islower(text[i]))
                    {
                        text[i] = text[i] + k;
                        if (text[i] > 'z')
                        {
                            text[i] = text[i] - 26;
                            printf("%c", text[i]);
                        }
                        else                        
                        printf("%c", text[i]);
                    }
                    else if (isspace(text[i]))
                    {
                        printf(" ");
                        if (isupper(text[i + 1]))
                        {
                            text[i + 1] = text[i + 1] + k;
                            if (text[i + 1] > 'Z')
                            {
                                text[i + 1] = text[i + 1] - 26;
                                printf("%c", text[i + 1]);
                            }
                            else
                            printf("%c", text[i + 1]);
                        }
                        else if (islower(text[i + 1]))
                        {
                            text[i + 1] = text[i + 1] + k;
                            if (text[i + 1] > 'z')
                            {
                                text[i + 1] = text[i + 1] - 26;
                                printf("%c", text[i + 1]);
                            }
                            else
                            printf("%c", text[i + 1]);
                        }
                        i++;
                    } 
                }
                else
                printf("%c", text[i]);
            }
            printf("\n");
            return 0;
        }
        else
        printf("Usage: ./caesar <non-negative integer>\n");
        return 1;        
    }
    else 
    printf("Usage: ./caesar <non-negative integer>\n");
    return 1;    
}

当我在终端中输入“./caesar 13”(13 是加密 key )时，系统会提示我输入所需的文本。但是，当我输入“matteo maTTeo”时，我得到的输出是:“znrb znGGrb”。为什么会这样呢？我对编码还很陌生，所以如果答案很明显，请对我放轻松!谢谢!

Answer 1

                   ...
                    if (isupper(text[i + 1]))
                    {
                        text[i + 1] = text[i + 1] + k;
                        if (text[i + 1] > 'Z')
                        {
                            text[i + 1] = text[i + 1] - 26;
                            printf("%c", text[i + 1]);
                        }
                        else
                        printf("%c", text[i + 1]);
                    }
                    else if (islower(text[i + 1]))
                    {
                        text[i + 1] = text[i + 1] + k;
                        if (text[i + 1] > 'z')
                        {
                            text[i + 1] = text[i + 1] - 26;
                            printf("%c", text[i + 1]);
                        }
                        else
                        printf("%c", text[i + 1]);
                    }
                    i++;
                    ......

在检查空格的情况下不需要此代码。它将在下一次迭代中自动处理。