#Java 7, 68 65 bytes
void c(int i){for(int x=0;x++<i;)System.out.print(i%2<1?92:'/');}
3 bytes saved thanks to @user902383 and @SeanBean.
Just like with this answer, the shortest code-golf seems to loop and print. Both recursive and
void c(int i){System.out.print(new String(new char[i]).replace("\0",i%2<1?"\\":"/"));}
seems to be longer.
Ungolfed & test code:
class M{
static void c(int i){
for(int x = 0; x++ < i;){
System.out.print(i % 2 < 1
? 92
: '/');
}
}
public static void main(String[] a){
for(int i = 0; i < 10; i++){
c(i);
System.out.println();
}
}
}
Output:
/
\\
///
\\\\
/////
\\\\\\
///////
\\\\\\\\
/////////