CS50 PSET 2 Caesar错误结果

使用23作为密钥将“barfoo”加密为“yxocll” 输出无效的ASCII文本 日志 正在运行/凯撒23。。。 正在检查输出“密文:yxocll”。。。

有人看到我的代码有什么问题吗?它似乎对大写字母很有效,但对于小写字母和某些“键”,我得到了错误的结果,并且无法找出原因。任何帮助都将不胜感激。

例子: 如果我试图用17的密钥加密“foo”,它应该返回“wff”,但我的代码只返回“w”。用我写的代码,它是说去位置128,这不是一个字母,但我的代码是说,如果超过122,扣除26。等于并返回“102”,即“f”。这与删除被分配到127有关吗

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

int main(int argc, string argv[])
{
  if (argc == 2) {
    int a = atoi (argv[1]);
    int b = a%26;
    printf("plaintext: ");
    //get string
    string s = get_string();
    printf ("ciphertext: ");
        //iterate through string
        for (int i=0, n =strlen(s); i<n; i++) {
            //check if character is a letter
            if ( isalpha (s[i])) {
                //check if letter is uppercase
                if (isupper (s[i])) {
                    //calculate position of character in ASCI by adding 'Key'. If character is over 90, decrease character location by 26
                    char c = (s[i] + b);
                    if (c > 90) {
                            char d = c - 26;
                            printf ("%c", d);
                    } else
                    printf("%c", c);
                } else
               //For lowercase letters. If character location is over position 122, decrease location by 26
                {
                    char e = (s[i] + b);
                    if (e>122) {
                            char f = e - 26;
                            printf("%c", f);
                    } else
                        printf("%c", e);
                }
            } else    //print non letters with no change made
            {
                printf ("%c", s[i]);
            }
        }
    }
printf ("\n");
return 0;