Updated to reverse the result of OP's loop
This makes a list (which needs to be reversed):
Q = Quotient[n, 2];
result = {};
While[Q != 0, AppendTo[result, Mod[n, 2]]; Q = Quotient[n, 2]; n = Q]
resultReverse[result]
{1, 0, 1, 0, 1}
If you want a string:
StringJoin[ToString /@ result]Reverse[result]]
"1011""1101"
There's also
BaseForm[13, 2]
IntegerString[13, 2]
"1101"
This makes a list:
Q = Quotient[n, 2];
result = {};
While[Q != 0, AppendTo[result, Mod[n, 2]]; Q = Quotient[n, 2]; n = Q]
result
{1, 0, 1, 1}
If you want a string:
StringJoin[ToString /@ result]
"1011"
There's also
BaseForm[13, 2]
IntegerString[13, 2]
"1101"
Updated to reverse the result of OP's loop
This makes a list (which needs to be reversed):
Q = Quotient[n, 2];
result = {};
While[Q != 0, AppendTo[result, Mod[n, 2]]; Q = Quotient[n, 2]; n = Q]
Reverse[result]
{1, 1, 0, 1}
If you want a string:
StringJoin[ToString /@ Reverse[result]]
"1101"
There's also
BaseForm[13, 2]
IntegerString[13, 2]
"1101"