Implement the strcat function

Implement the strcat function as efficiently as you can..
How do you handle errors if you had to

VERY SIMPLE & EFFICIENT CODE

void strcat(char *str1,char *str2)
{

while(*str1++)
;
while((*str1++ = *str2++) != '\0')
;
}

Implement the strcat function

[code:1]char * str_cat(char *src, char*dest)

{
int i=0;
int len= strlen(src);
while(dest[i]!='\0')
{
i++;
}

for(int j=0;j<=len;j++)
{
dest[i]=src[j];
i++;
}
return dest;
}[/code:1]