0^0 is the value of the function x^x when x=0. In fact, x^x is not defined at 0 (not in the domain of definition), therefore 0^0 is not defined. But, we can say that the limit of x^x as x tends to zero equals to 1,yet we can not say that 0^0=1. Programming languages evaluates this limit -not the value- as 1. Finally 0^0 is not defined, but the limit of x^x as x tends to 0 is 1.