#include <stdio.h>
#include <string.h>
char* reversal(char* str,size_t len)
{
    if(str != NULL)
    {
        char* start =  str;
        char* end   = str + len - 1;
        char ch;
        while(start < end) //注意这里的条件不能是start != end;因为大小如果是偶数的话,它们永远不会相等.
        {
            ch = *start;
            *start++ = *end;
            *end-- = ch;
        }
    }
    return str;
}
int main(void)
{
    char str[] = "abcdefg";
    size_t len = strlen(str);
    reversal(str,len);
    printf("%s\n",str);
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <assert.h>
char* reversal_str(char* const dest,const char* src,size_t len)
{
    assert(dest != NULL && src != NULL);
    char* start = dest;
    char*   end = dest + len - 1;
    char ch;
    strcpy(dest,src);//把它拷贝到dest内存中.
    while(start < end) //注意这里不能写成start != end;
    {
        ch = *start;      //交换首尾字符
        *start++ = *end;
        *end-- = ch;
    }
    return dest;
}

int main(void)
{
    char *str1 = "abcdefg";
    char str2[] = "1234567";
    char str[100] = {};
    size_t len = strlen(str1);
    reversal_str(str,str1,len);
    printf("%s\n",str);
    len = strlen(str2);
    reversal_str(str,str2,len);
    printf("%s\n",str);
    return 0;
}

#include <stdio.h>

void shift_base(int num,size_t base)
{
    int arr[32] = {},i = 0;
    do
    {
        arr[i++] = num % base;
    }while(num /= base);
    printf("它的%d进制的格式是:\n",base);
    for(num = i - 1;num >= 0;num--)
        arr[num] < 10?printf("%d",arr[num]):
            printf("%c",arr[num]-10+'A');
    printf("\n");
}
int main(void)
{
    int num = 0;
    size_t base = 0;
    printf("请输入一个整数:");
    scanf("%d",&num);
    printf("你输入你要打印的进制数:");
    scanf("%d",&base);
    shift_base(num,base);
    return 0;
}

#include <stdio.h>

long factial(int n)
{
    static long fac = 1;
    int i = 0;
    fac *= n;
    return fac;
}
long sum_fac(int n)
{
    int i;
    static long sum = 0;
    for(i = 1;i <= n;i++)
    {
        sum += factial(i);
    }
    return sum;
}
int main(void)
{
    int n;
    printf("请输入你要求的阶乘数:");
    scanf("%d",&n);
    printf("1!+2!+...%d! = %ld\n",n,sum_fac(n));
    return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int main(void)
{
    float a = 1.0f;
    cout << (int)a << endl;
    cout << &a << endl;
    cout << (int&)a << endl;
    cout << boolalpha << ((int)a == (int&)a) << endl;
    float b = 0.0f;
    cout << (int)b << endl;
    cout << &b << endl;
    cout << (int&)b << endl;
    cout << boolalpha << ((int)b == (int&)b) << endl;
    return 0;
}

#include <stdio.h>
int main(void)
{
    unsigned int a  = 0xFFFFFFF7;
    unsigned char i = (unsigned char)a; 
    char* b = (char*)&a; 
    printf("%08x,%08x\n",i,*b);
    return 0;
}

int  fun(int x,int y)
{
           return (x&y) + ((x^y)>>1)   
}
fun(144,296) = _____________?