1. 请编程实现二维数组的杨辉三角

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


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

    int a[n][n];
    memset(a, 0, sizeof(a));
    a[0][0] = 1;

    for (int i = 1; i < n; i++)
    {
        for (int j = 0; j < i + 1; j++)
        {
            if (0 == j)
            {
                a[i][j] = 1;
            }
            else
            {
                a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
            }
        }
    }

    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < i + 1; j++)
        {
            printf("%4d", a[i][j]);
        }
        puts("");
    }
}

2. 请编程实现二维数组计算每一行和以及列和

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


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

    int a[n][n];
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            scanf("%d", &a[i][j]);
        }
    }

    printf("行和：");
    for (int i = 0; i < n; i++)
    {
        int sum = 0;
        for (int j = 0; j < n; j++)
        {
            sum += a[i][j];
        }
        printf("%4d", sum);
    }
    puts("");

    printf("列和：");
    for (int i = 0; i < n; i++)
    {
        int sum = 0;
        for (int j = 0; j < n; j++)
        {
            sum += a[j][i];
        }
        printf("%4d", sum);
    }
    puts("");

    return 0;
}

3. 请编程实现二维数组计算第二大值

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


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

    int a[n][n];
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            scanf("%d", &a[i][j]);
        }
    }

    int max = 0;
    for (int i = 0; i < n; i++)
    {

        for (int j = 0; j < n; j++)
        {
            if (max < a[i][j])
            {
                max = a[i][j];
            }
        }
    }


    int sec_max = 0;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            if (sec_max < a[i][j] && max > a[i][j])
            {
                sec_max = a[i][j];
            }
        }
    }
    printf("第二大：%d\n", sec_max);

    return 0;
}

4. 请使用非函数方法实现系统函数strcat，strcmp，strcpy，strlen

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

void my_strcmp(char s1[], char s2[])
{
    int i = 0;
    while (s1[i] == s2[i])
    {
        if (s1[i] == '\0' || s2[i] == '\0')
        {
            break;
        }
        i++;
    }

    if (s1[i] > s2[i])
    {
        puts("s1 > s2");
    }
    else if (s1[i] < s2[i])
    {
        puts("s1 < s2");
    }
    else
    {
        puts("s1 == s2");
    }
}

void my_strcpy(char s1[], char s2[])
{
    int i = 0;
    while (s2[i] != '\0')
    {
        s1[i] = s2[i];
        i++;
    }
    s1[i] = '\0';
}

int my_strlen(char s[])
{
    int i;
    for (i = 0; s[i] != '\0'; i++);

    return i;
}

void my_strcat(char s1[], char s2[])
{
    int i = 0;
    while (s1[i] != '\0')
    {
        i++;
    }

    int j = 0;
    while (s2[j] != '\0')
    {
        s1[i + j] = s2[j];
        j++;
    }

    s1[i + j] = '\0';
}

int main()
{
    char s1[20] = "hello";
    char s2[20] = "world";

    my_strcmp(s1, s2);
    printf("%s len: %d\n", s1, my_strlen(s1));
    my_strcpy(s1, s2);
    printf("%s\n", s1);
    my_strcat(s1, s2);
    printf("%s\n", s1);


    return 0;
}