关于玩手机的警示语:C语言编程:用自定义函数实现字符串处理函数strcat、 strcpy、strcmp、strlen和

char *mystrcat(char *dst, char *src)
{
char *p = dst;
while(*p)++p;
while(*p++ = *src++);
return dst;
}
char *mystrcpy(char *dst, char *src)
{
while(*dst++ = *src++);
return dst;
}
int mystrcmp(char *dst, char *src)
{
while(*dst && *dst == *src)
{
++dst;
++src;
}
return *dst - *src;
}
int mystrlen(char *dst)
{
char *p = dst;
while(*p)++p;
return p - dst;
}
int main()
{
char s[32], t[32] = "HELLO,CHINA";
mystrcpy(s, "HELLO,");
puts(s);
mystrcat(s, "USA");
puts(s);

printf("%d %d\n", mystrlen(s), mystrcmp(s, t));
}

void strcat(char s1[],char s2[])
{int i,j;
for(i=0;s1[i]!='\0';i++);
for(j=0;s2[j]!='\0';j++)
s1[i++]=s2[j];
s1[i]='\0';
}
void strcpy(char a[],char b[])
{
int i=0,j=0;
while((a[i++]=b[j++])!='\0');}
int strcmp(char s1[],char s2[])
{int i;
for(i=0;s1[i]!='\0'&&s2[i]!='\0';i++)
{
if(s1[i]>s2[i])
return 1;
else if(s1[i]<s2[i])
return -1;}
if(s1[i]=='\0'&&s2[i]=='\0')
return 0;
else if(s1[i]=='\0')
return -1;
else
return 1;
}
int strlen(char s[])
{
int len=0 ,i;
for(i=0;s[i]!='\0';i++)
len++;
return len;}

char* strcat( char s1[], const char s2[] )
{
if (s1==NULL || s2==NULL)
return NULL;
for(char* p=s1+sizeof(s1)-1; *s2!='\0'; p++,s2++)
*p = *s2;
return s1;
}