String instances in C

1. #include <stdio.h>
#include <assert.h>

size_t strlen (const char* s)
{
Return (assert (s), (*s? (Strlen (s+1) + 1): 0));
}

int main ()
{
printf ("%d\n", strlen (NULL));

return 0;
}

2. #include <stdio.h>
#include <assert.h>

char* strcpy (char* DST, const char* src)
{
    char* ret = DST;
    
    assert (DST && src);//Assert must invoke Assert, which is the idea of safe programming, the idea of error handling
    
    while ((*dst++ = *src++)! = ' + ');
    
    return ret;
}

Int main ()
{
    char dst[20];
    
    printf ("%s\n", strcpy (DST, "Delphi tang!"));
    getch ();    
    return 0;

}

3. #include <stdio.h>
#include <malloc.h>

Int main ()
{
    char s1[] = { ' H ', ' e ', ' l ', ' l ', ' o '};
    char s2[] = {' H ', ' e ', ' l ', ' l ', ' o ', ' n '};
    char* s3 = "Hello";         //read-only store
    char* S4 = (char*) malloc (6*sizeof (char)); Heap
    
    s4[0] = ' H ';
    s4[1] = ' e ';
    s4[2] = ' l ';
    s4[3] = ' l ';
    s4[4] = ' o ';
    s4[5] = ' + ';
    
    Free (S4);
    
    return 0;
}

4. #include <stdio.h>
#include <assert.h>

size_t strlen (const char* s)
{
size_t length = 0;

ASSERT (s);

while (*s++)
{
length++;
}

return length;
}

int main ()
{
printf ("%d\n", strlen ("123456789"));

return 0;
}

String instances in C