Question

3、用自定义函数实现字符串处理函数strcat、 strcpy、strcmp、strlen和strlwr的功能。

Answer 1

1.strcat
void mycat(char *s1, char *s2)
{
while(*s1++);
s1--;
while(*s1++ = *s2++);
}
2.strcpy
void mycpy(char *s1, char *s2)
{
while(*s1++ = *s2++);
}
3.strcmp
int mycmp(char *s1,char *s2)
{
for( ; *s == *t;s++,t++)
if(*s == 0) return 0;
return *s - *t;
}
4.strlen
int mylen(char *s1)
{
char *p = s1;
while(*p++);
return p - s -1;
}
5.strlwr
char* strlwr(char *s)
{ unsigned char AL;
register char *DX,*SI;
DX=SI=s;
while((AL=*SI++)!='\0')
{ AL-='A';
if(AL>'Z'-'A')continue;
SI[-1]+='a'-'A';
}
return DX;
}