#include <stdio.h>

int main()
{
    int a[5] = {1, 2, 3, 4, 5};
    int* p1 = (int*)(&a + 1); // <==> (unsigned int)&a+sizeof(*&a) => 整个数组后面的那个地址
    int* p2 = (int*)((int)a + 1); <=> 取a[0]后三个字节拼接a[1]第一个字节 => 0x02000000
    int* p3 = (int*)(a + 1); <=> a[2]
    
    printf("%d\n", p1[-1]); // (unsigned int)p1-1*sizeof(*p1) => a[4]
    printf("%d\n", p2[0]);  //  0x02000000
    printf("%d\n", p3[1]); // a[3]
    
    return 0;
}

return (assert(s), (*s ? strlen(s+1)+1 : 0));

#size_t为无符号整数 strlen的返回值为 size_t 类型
size_t strlen(const char* s)
{
    size_t length = 0;
    aasert(s);//当指针为空时运行出错 assert.h 
    
    while(*s++)
    {
        length++;
    }
    return 
    
}

#include <stdio.h>
#include <assert.h>

char* strcpy(char* dst, const char* src)
{
    char* ret = dst;
    
    assert(dst && src);
    
    while( (*dst++ = *src++) != '\0' );
    
    return ret;
}

int main()
{
    char dst[20];
    
    printf("%s\n", strcpy(dst, "Delphi Tang!"));
    
    return 0;
}

#include <stdio.h>
#include <malloc.h>

int reset(char**p, int size, int new_size)
{
    int ret = 1;
    int i = 0;
    int len = 0;
    char* pt = NULL;
    char* tmp = NULL;
    char* pp = *p;
    
    if( (p != NULL) && (new_size > 0) )
    {
        pt = (char*)malloc(new_size);
        
        tmp = pt;
        
        len = (size < new_size) ? size : new_size;
        
        for(i=0; i<len; i++)
        {
            *tmp++ = *pp++;      
        }
        
        free(*p);
        *p = pt;
    }
    else
    {
        ret = 0;
    }
    
    return ret;
}

int main()
{
    char* p = (char*)malloc(5);
    
    printf("%0X\n", p);
    
    if( reset(&p, 5, 3) )
    {
        printf("%0X\n", p);
    }
    
    return 0;
}

#include <stdio.h>
#include <malloc.h>

void printArray(int a[], int size)
{
    int i = 0;
    
    printf("printArray: %d\n", sizeof(a));

    for(i=0; i<size; i++)
    {
        printf("%d\n", a[i]);
    }
}

int main()
{
    int a[3][3] = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
    int* p = &a[0][0];
    
    printArray(p, 9);
    
    return 0;
}

#include <stdio.h>

int main(int argc, char* argv[], char* env[])
{
    int a[3][3] = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
    int i = 0;
    int j = 0;
    
    for(i=0; i<3; i++)
    {
        for(j=0; j<3; j++)
        {
            printf("%d\n", *(*(a+i) + j));
        }
    }
}

#include <stdio.h>

int main()
{
    int a[5][5];
    int(*p)[4];
    
    p = a;
    
    printf("%d\n", &p[4][2] - &a[4][2]); // -4
}

#include <stdio.h>

int main()
{ 
    int (*p2)(int*, int (*f)(int*));
    
    int (*p3[5])(int*);
    
    int (*(*p4)[5])(int*);
    
    int (*(*p5)(int*))[5];
}

#include "stdio.h"
int test(int i)
{
        return i;
}

int (*test(int *p))[5]  //返回类型为 int(*)[5]
{
        static int a[5]={1,2,3,4,5};    
        return &a;
}

int main(int argc, char** argv, char*  env[])  
{

        int (*(*p5)(int*))[5];
        int a = 1;
        //p5 = &a;
        p5 = test; 

        int(*p)[5] = p5(&a); 

        printf("%d \n", *(*p+1));
        printf("%d \n", *(*p+2));

        return 0;
}

int **malloc2d(int row, int col)
{
    int** ret = (int**)malloc(sizeof(int*)*row);
    int* p = (int*)malloc(sizeof(int)*row*col);

    int i = 0;
    if (ret && p)
    {
        for (i = 0; i < row;i++)
        {
            ret[i] = (p + i*col);
        }
    }
    else{
        free(p);
        free(ret);
    }

    return ret;
}

void free2d(int **a)
{
    free(a[0]);
    free(a);
}

#include <stdio.h>

void access(int a[][3], int row) 
{
    //没必要传递列，可以计算出来,c语言中只有一维数组

    int col = sizeof(*a) / sizeof(int);
    int i = 0;
    int j = 0;
    
    printf("sizeof(a) = %d\n", sizeof(a));
    
    for(i=0; i<row; i++)
    {
        for(j=0; j<col; j++)
        {
            printf("%d\n", a[i][j]);
        }
    }
}

int main()
{
    int a[3][3] = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
    
    access(a, 3);
}

#include <stdio.h>
#include <stdarg.h>

float average(int n, ...)
{
    va_list args;
    int i = 0;
    float sum = 0;
    
    va_start(args, n);
    
    for(i=0; i<n; i++)
    {
        sum += va_arg(args, int);
    }
    
    va_end(args);
    
    return sum / n;
}

int main()
{
    printf("%f\n", average(5, 1, 2, 3, 4, 5));
    printf("%f\n", average(4, 1, 2, 3, 4));
    
    return 0;
}

#include <stdio.h>

#define RESET(p, len) while( len > 0) ((char*)p)[--len] = 0

void reset(void* p, int len)
{
    while( len > 0 ) 
    {
        ((char*)p)[--len] = 0;
    }
}

int main()
{
    int array[] = {1, 2, 3, 4, 5};
    int len = sizeof(array);
    
    reset(array, len);
    RESET(array, len);
    
    return 0;
}