C语言这两道题不会写呀，能康康嘛。

3

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

#define N 256

int main()
{
    char s[N];
    fgets(s, N, stdin);
    const char *p = s;
    while (*p == ' ')
        p++;
    if (p != s)
        strcpy(s, p);
    printf("%s", s);
    return 0;
}

4

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

#define M 10
#define N 15

void merge(int sa[], int na, int sb[], int nb)
{
    int *pa = sa + na - 1;
    int *pb = sb + nb - 1;
    int *q = sa + na + nb - 1;
    while (pa >= sa && pb >= sb)
    {
        if (*pa > *pb)
        {
            *q-- = *pa--;
        }
        else if (*pb > *pa)
        {
            *q-- = *pb--;
        }
        else
        {
            *q-- = *pa--;
            *q-- = *pb--;
        }
    }
    while (pa >= sa)
        *q-- = *pa--;
    while (pb >= sb)
        *q-- = *pb--;
}

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

int main()
{
    int a[N + M], b[N];

    srand(time(NULL));
    for (int i = 0; i < M; i++)
        a[i] = rand() % 100;
    for (int i = 0; i < N; i++)
        b[i] = rand() % 100;
    sort(a, M);
    sort(b, N);

    printf("a[%d]: ", M);
    for (int i = 0; i < M; i++)
        printf("%d ", a[i]);
    printf("\n");

    printf("b[%d]: ", N);
    for (int i = 0; i < N; i++)
        printf("%d ", b[i]);
    printf("\n");

    merge(a, M, b, N);
    printf("after merge a and b:\n");
    for (int i = 0; i < M + N; i++)
        printf("%d ", a[i]);
    printf("\n");

    return 0;
}