程序代码：

# include <stdio.h>
# include <string.h>
# define M 5
# define N 20

void fun(char (*ss)[N])
{
    int i, j, n, k, len, m;

    //用来寻找出长度最长的字符串，并且标出其序列号。
    for (i=0; i<M; i++)
    {
        len = strlen(ss[i]);

        if (i == 0)
            n = len;
        if (len > n)
        {
            n = len;
            k = i;
        }
    }
    //对于i!=k的字符串，从后往前先依次赋值，后将剩余的位置全部加*号。
    for (i=0; i<M; i++)
    {
        if (i != k)
        {
            len = strlen(ss[i]);

            for (j=len; j>=0; j--)
            {
                ss[i][m] = ss[i][j];
                m--;
            }
            for (j=0; j<n-len; j++)
                ss[i][j] = '*';
        }
    }
}

int main(void)
{
    char ss[M][N] = {"shanghai", "guangzhou", "beijing", "tianjing", "chongqing"};
    int i;

    printf("\nThe original strings are : \n");
    for (i=0; i<M; i++)
        printf("%s\n", ss[i]);
    printf("\n");

    fun(ss);

    printf("\nThe result : \n");
    for (i=0; i<M; i++)
        printf("%s\n", ss[i]);

    return 0;
}