二进制是Binary，简写为B。
八进制是Octal，简写为O。
十进制为Decimal，简写为D。
十六进制为Hexadecimal，简写为H。
八进制是Octal，简写为O。
十进制为Decimal，简写为D。
十六进制为Hexadecimal，简写为H。
一、求二进制中1的个数：
int f(unsigned int n)
{ unsigned int number=0;for(number=0;n;++number){n&=(n-1); //每与一次就少一个1}return number; //number即为二进制中1的个数
}二、求二进制中0的个数：int f(unsigned int n)
{unsigned int number = 0;while(n != 0) {if((n&1)==0)number++;n>>=1;}return number; //number即二进制中0的个数
}三、返回数组中最大值的下标
#include <stdio.h>
int fun ( int * s,int n ) //n为指针s的长度
{ int i,k;for ( i＝0, k ＝ i; i < n; i++)if ( s[i] > s[k]) k = i;return (k);
}四、选择排序（降序）
int a[]={4,0,2,3,1},i,j,t;
for(i=1;i<5;i++)
{t=a[i];j=i-1;while(j>=0&&t>a[j]){a[j+1]=a[j];--j;}a[j+1]=t;
}五、将十六进制的字符串转化为二进制的字符串
int i = 1024;
char bs[16],b[16];
sscanf(hs,"%x",&i);
itoa(i,b,2);
sprintf(bs,"%016s",b);
printf("\nhs=%s,bs=%s\n",hs,bs); //hs为原始的十六进制，bs为转化完成的二进制字符串
void itoa(unsigned long val,char *buf,unsigned radix) //buf为转化完成的二进制字符串
{char *p; /* pointer to traverse string */char *firstdig; /* pointer to first digit */char temp; /* temp char */unsigned digval; /* value of digit */p = buf;firstdig = p; /* save pointer to first digit */do{digval = (unsigned)(val%radix);val /= radix; /* get next digit */
/* convert to ascii and store */if(digval > 9)*p++ = (char)(digval - 10 + 'a'); /* a letter */else*p++ = (char)(digval + '0'); /* a digit */}while(val>0);/* We now have the digit of the number in the buffer, but in reverse order. Thus we reverse them now. */*p-- = '\0'; /* terminate string; p points to last digit */do{temp = *p;*p = *firstdig;*firstdig = temp; /* swap *p and *firstdig */--p;++firstdig; /* advance to next two digits */
}while(firstdig < p); /* repeat until halfway */
}六、字符串转化为十六进制
pbDest1为输出的十六进制 pbSrc1为输入的字符串
/*
// C prototype : void StrToHex(byte *pbDest, char *pszSrc, int nLen)
// parameter(s): [OUT] pbDest - 输出缓冲区
// [IN] pszSrc - 字符串
// [IN] nLen - 16进制数的字节数(字符串的长度/2)
// return value:
// remarks : 将字符串转化为16进制数
*/
void StrToHex( char *pbDest1, char *pbSrc1, int nLen)
{char h1,h2;unsigned char s1,s2;int i;for (i=0; i<nLen; i++){h1 = pbSrc1[2*i];h2 = pbSrc1[2*i+1];s1 = toupper(h1) - 0x30;if (s1 > 9)s1 -= 7;s2 = toupper(h2) - 0x30;if (s2 > 9)s2 -= 7;pbDest1[i] = s1*16 + s2;}
}七、十六进制转化为字符串
pbDest2为输出的字符串 pbSrc2为输入的十六进制
/*
// C prototype : void HexToStr(char *pszDest, byte *pbSrc, int nLen)
// parameter(s): [OUT] pszDest - 存放目标字符串
// [IN] pbSrc - 输入16进制数的起始地址
// [IN] nLen - 16进制数的字节数
// return value:
// remarks : 将16进制数转化为字符串
*/
void HexToStr( char *pbDest2, unsigned char *pbSrc2, int nLen)
{char ddl,ddh;int i;for (i=0; i<nLen; i++){ddh = 48 + pbSrc2[i] / 16;ddl = 48 + pbSrc2[i] % 16;if (ddh > 57) ddh = ddh + 7;if (ddl > 57) ddl = ddl + 7;pbDest2[i*2] = ddh;pbDest2[i*2+1] = ddl;} pbDest2[nLen*2] = '\0';
}八、十六进制字符串转化为十进制数
int tolower(int c)
{if (c >= 'A' && c <= 'Z'){return c + 'a' - 'A';}else{return c;}
}int htoi(char s[])
{int i;int n = 0;if (s[0] == '0' && (s[1]=='x' || s[1]=='X')){i = 2;}else{i = 0;}for (; (s[i] >= '0' && s[i] <= '9') || (s[i] >= 'a' && s[i] <= 'z') || (s[i] >='A' && s[i] <= 'Z');++i){if (tolower(s[i]) > '9'){n = 16 * n + (10 + tolower(s[i]) - 'a');}else{n = 16 * n + (tolower(s[i]) - '0');}}return n;
}
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