What is one one and on to function?

plz...

explain with example.........

Thanks

A function from A to B is said to be one one function if no two elements in A have same image in B.

Ex. A={a,b,c} and B={1,2,3,4}

   and f:A to B = {(a,1),(b,2),(c,3)} is a one one function

                          range:{1,2,3} ; codomain:{1,2,3,4}

   but g:A to B = {(a,1),(b,1),(c,2)} is not one one function as 'a' and 'b' has same image i.e. 1

A function is said to be onto if the range is equal to its codomain

A={a,b,c,d} and B={1,2,3,4}

   and f:A to B = {(a,1),(b,2),(c,3),(d,4)} is a onto function

                          range:{1,2,3,4} = codomain:{1,2,3,4}

   but g:A to B = {(a,1),(b,1),(c,2)} is not onto function

                            range:{1,2} is not equal to codomain