这个用c语言怎么写，求解答！

供参考：

#include<stdio.h>
int main()
{
    char a[256];
    int  i = 0, k = 0;
    scanf("%s%d", a, &k);
    while (a[i] != '\0')
    {
        if (a[i] >= 'A' && a[i] <= 'Z')
            a[i] = (a[i] - 'A' + k) % 26 + 'A';
        else if (a[i] >= 'a' && a[i] <= 'z')
            a[i] = (a[i] - 'a' + k) % 26 + 'a';
        i++;
    }
    a[i] = '\0';
    printf("%s\n", a);
    return 0;
}