bankpro, the function atoi just recognises
1) An optional string of tabs or spaces
2) An optional sign &
3) A string of digits

And upon recognising it converts it to int otherwise on failure it returns 0.
So if u try to convert a string like "name" u'll b getting 0 as it doesn't recognise it. If u try something like "22" or "-22" or even " -22" it would return int (here 22 or -22 as the case be).
I hope this clears ur doubt