#include <stdio.h>

void main()
{
    char a[5][5] = {
        {' ', ' ', '1', ' ', ' '},
        {' ', '1', '2', '1', ' '},
        {'1', '2', '3', '2', '1'},
        {' ', '1', '2', '1', ' '},
        {' ', ' ', '1', ' ', ' '}
    };
    int i, j;
    for(i = 0; i < 5; i++)
    {
        printf("\n");
        for(j = 0; j < 5; j++)
        {
            printf("%c", a[i][j]);
        }
    }
}

#include <stdio.h>

void main()
{
    char a[40];
    int i, n = 0;

    do {
        scanf("%c", &a[n]);
        n++;
    } while (a[n - 1] != '\n');

    n = n - 1; // n是输入字符数目。不含\n

    for(i = 0; i < n; i++)
        if(('A' <= a[i]) && (a[i] <= 'Z'))
            a[i] += 32; // 是大写字母改为对应的小写字母

    for(i = n - 1; i >= 0; i--)
        printf("%c", a[i]);
}

#include <stdio.h>

void main()
{
    char a[80];
    int n = 0;
    scanf("%s", a);
    while(a[n] != '\0')
        n++;
    printf("length of %s = %d\n", a, n);
}

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

void main()
{
    char a[40], b[80];
    gets(a);
    strcpy(b, a);
    strcat(b, a);

    if(strcmp(a, b) < 0)
        printf("a < b\n");
    else if(strcmp(a, b) > 0)
        printf("a > b\n");
    else
        printf("a = b\n");

    printf("length of a(%s) = %d\n", a, strlen(a));
    printf("length of b(%s) = %d\n", b, strlen(b));
    puts(a);
    puts(b);

}