C语言-重写strlen, strcpy, strcat, strcmp方法

//一、数组版本
int stringLength(char arr[])
{
   int i =0;
   while(arr[i])
        i++;
   return i;
}

char *stringCopy(char arr1[],char arr2[])
{
   int i = 0;
   while((arr1[i] = arr2[i]) !='\0')
        i++;
   return arr1[];
}

char *stringCatch(char arr1[],char arr2[])
{
   int i =0, j =0;
   while(arr1[i])
        i++;
   while((arr1[i + j] = arr2[j]) !='\0')
        j++;
   return arr1;
}

int stringCompare(char arr1[],char arr2[])
{
   int i = 0;
   while(arr1[i] == arr2[i]) {
       if(!arr1[i])
           return 0;
        i++;
    }
   returnarr1[i] - arr2[i];
}


//二、指针版本

int stringLength(char *s)
{
   int i =0;
   while(*s++)
        i++;
   return i;
}

void stringCopy(char *s,char *t)
{
   while((*s++ = *t++));
}

//stringCatch方法，这里假设 s的空间足够大，’\0’之后的内存存储的都是’\0'
void stringCatch(char *s,char *t)
{
//    for( ; *t != '\0'; s++) {
//        if(*s == '\0') {
//            *s = *t;
//            t++;
//        }
//    }
    while (*t) {
        if (!*s) {
            *s = *t;
            t++;
        }
        s++;
    }
}

int stringCompare(char *s,char *t)
{
   int i = 0;
   for( ; *s == *t; s++, t++)
       if(*s == '\0')
           return 0;
   return *s - *t;
}