编C语言程序：用自定义函数实现字符串处理函数strcat、 strcpy、strcmp、strlen和strlwr的功能

/***
*char *strcat(dst, src) - concatenate (append) one string to another
*
*Purpose:
* Concatenates src onto the end of dest. Assumes enough
* space in dest.
*
*Entry:
* char *dst - string to which "src" is to be appended
* const char *src - string to be appended to the end of "dst"
*
*Exit:
* The address of "dst"
*
*Exceptions:
*
*******************************************************************************/

char * __cdecl strcat (
char * dst,
const char * src
)
{
char * cp = dst;

while( *cp )
cp++; /* find end of dst */

while( *cp++ = *src++ ) ; /* Copy src to end of dst */

return( dst ); /* return dst */

}

/***
*char *strcpy(dst, src) - copy one string over another
*
*Purpose:
* Copies the string src into the spot specified by
* dest; assumes enough room.
*
*Entry:
* char * dst - string over which "src" is to be copied
* const char * src - string to be copied over "dst"
*
*Exit:
* The address of "dst"
*
*Exceptions:
*******************************************************************************/

char * __cdecl strcpy(char * dst, const char * src)
{
char * cp = dst;

while( *cp++ = *src++ )
; /* Copy src over dst */

return( dst );
}
//以上是微软的实现，更多的到VC++安装盘下CRT目录找吧

strlen(char *str)
{
int n=0;
char *p=str;
while(*p++)n++;
return n;
}
strcat(char *str1,str2)
{
char *p1,*p2;
p1=str1;
p2=str2;
p1+=strlen(str1);
while(*p2)
*p1++=*p2++;
return
}
strcpy(char *str1,str2)
{
char *p1,*p2;
p1=str1;
p2=str2;
while(*p2)
*p1++=*p2++;
return

}
strcmp(char *str1,str2)
{
char *p1,*p2;
p1=str1;
p2=str2;
while(*p2 && *p1)
if(*(p1++)- *(p2++) )return *(p1++)- *(p2++) ;
return 0;

}

其它同理！！！！！！！！！

呵呵!昨天刚答过,不会是作业吧!

http://zhidao.baidu.com/question/7908569.html

void strlwr(char s[])
{int i;
for(i=0;s!='\0';i++)
if(s>='A'&&s<='Z')
s=s+32;
}