1.strcat

voidmycat(char*s1,char*s2)

{

while(*s1++);

s1--;

while(*s1++=*s2++);

}

2.strcpy

voidmycpy(char*s1,char*s2)

{

while(*s1++=*s2++);

}

3.strcmp

intmycmp(char*s1,char*s2)

{

for(;*s==*t;s++,t++)

if(*s==0)return0;

return*s-*t;

}

4.strlen

intmylen(char*s1)

{

char*p=s1;

while(*p++);

returnp-s-1;

}

5.strlwr

char*strlwr(char*s)

{unsignedcharAL;

registerchar*DX,*SI;

DX=SI=s;

while((AL=*SI++)!="\0")

{AL-="A";

if(AL>"Z"-"A")continue;

SI[-1]+="a"-"A";

}

returnDX;

}