c语言程序相关的问题

c语言初学者 编写一个程序
输入一行字母 然后输入数字 最后打印数字对应的字母
如果是空格就输出空格 如果是字符就输出字符
例子

./c 
abcdefghijklmnopqrstuvwxyz
0
Is 'a'

./c 
abcdefghijklmnopqrstuvwxyz
2
Is 'c'

./c 
Are you ok?
3
Is ' '

./c 
Are you ok?
10
Is '?'

想问下怎么写
在Linux系统下

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

int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        printf("%s <string> ...\n", argv[0]);
        return 1;
    }

    char buffer[256];
    char *p = buffer;
    for (int i = 1; i < argc; i++)
    {
        strcpy(p, argv[i]);
        p += strlen(argv[i]);
        *p++ = ' ';
    }
    *p = '\0';

    int n;
    scanf("%d", &n);

    if (n >= 0 && n < strlen(buffer))
        printf("Is '%c'\n", buffer[n]);
    else
        printf("invalid index\n");

    return 0;
}

$ gcc -Wall main.c
$ ./a.out abcdefghijklmnopqrstuvwxyz
0
Is 'a'
$ ./a.out abcdefghijklmnopqrstuvwxyz
2
Is 'c' 
$ ./a.out Are you ok?
3
Is ' '
$ ./a.out Are you ok?
10
Is '?'

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