Question

Recently I attended an interview where they asked me to write a C program to concatenate two strings without using strcat(), strlen() and strcmp() and that function should not exceed two (2) lines.

I know how to concatenate two strings without using strcat(). But my method has nearly 15 lines. I dont know how to write it in two lines.

Answer 1

I expect they wanted something like this:

void mystrcat(char * dest, const char * src)
{
    //advance dest until we find the terminating null
    while (*dest) ++dest;

    //copy src to dest including terminating null, until we hit the end of src
    //Edit: originally this: 
    //for (; *dest = *src, *src; ++dest, ++src);
    //...which is the same as this
    for (; *dest = *src; ++dest, ++src);
}

It doesn’t return the end of the concatenated string like the real strcat, but that doesn’t seem to be required.

I don’t necessarily know if this sort of thing is a good interview question – it shows that you can code tersely, and that you know what strcat does, but that’s about it.

Edit: as aib writes, the statement

while (*dest++ = *src++);

…is perhaps a more conventional way of writing the second loop (instead of using for).