What does it mean when we use a variable in C++ like a function with a default value as its parameter? -

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i reading c++ code line. encountered weird code line variable used function 0 parameter!

template <class t> class stack {     t data[50];     int nelements; public: //this line variable used function!     stack() : nelements(0){}     void push(t elemen);     t pop();     int tamanho();     int isempty(); }; 

so mean when have: the constructor : private variable (0){}

this code line weird me! thanks

in initializer_list of stacks constructor, class member nelements initialized value of 0 upon creation of each stack object.

the value 0 not have special meaning here, other setting initial number of elements stack 0 gets created , empty.