Implement a function that takes two strings as arguments, a and b. It then creates a new string at least as long as both a and b. It compares a and b and outputs a new string that indicates how the two strings differ.

Pattern	Output
a[i] == b[i]	c[i] = =
a[i] > b[i]	c[i] = +
a[i] < b[i]	c[i] = -
i > len(a) and i <= len(b)	c[i] = ?
i > len(b) and i <= len(a)	c[i] = ?

Use the following prototype:

char * diff(const char *a, const char *b);

Here are some examples:

Input	Output
diff(aaab,aaac)	===-
diff(bbbbb,cc)	--???
diff(123, 012)	+++
diff(What?,)	?????

You may use functions in string.h.

Hint: you need to use malloc to allocate storage space for the new string, and return a pointer to the new array.