c语言程序相关的问题

c语言初学者
编写一个程序
要求将输入的字母转化对应的12345

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

#define N 256

int main(int argc, char *argv[])
{
    char s[N], m[128] = {0};
    if (argc != 2 || strlen(argv[1]) < 26)
    {
        printf("%s <26-letters>\n", argv[0]);
        return 1;
    }
    for (int i = 0; i < 26; i++)
    {
        m['a' + i] = tolower(argv[1][i]);
        m['A' + i] = toupper(argv[1][i]);
    }
    while (fgets(s, N, stdin))
    {
        const char *p = s;
        while (*p)
        {
            if (isalpha(*p))
                putchar(m[(int)*p]);
            else
                putchar(*p);
            p++;
        }
    }
    return 0;
}

$ gcc -Wall main.c
$ ./a.out qwertyuiopasdfghjklzxcvbnm
I was scared of dentists
O vql leqktr gy rtfzolzl