why is this not returning 4

[AL88]

I'm really confused as to why this is not returning 4. Help please :-)

  #include<iostream>

int difference(int a, int b);

int main()
{
int currentYear = 2018;

int graduationYear = 2022;

difference(currentYear,graduationYear);

std::cout << "The year is : " << currentYear << " \nYou graduate in year : "<< graduationYear<< " You have : "<<difference << " years to graduate.\n";

}

int difference(int a,int b)
{
int theDifference;
theDifference = (a-b);

return theDifference;
}
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[Peter87]

You don't do anything with the return value.

You either have to store the return value in a variable and then print it.

int yearsLeftTograduation = difference(graduationYear, currentYear);
std::cout << "You have : " << yearsLeftTograduation << " years to graduate.\n";

Or you can call the function directly when printing.

std::cout << "You have : " << difference(graduationYear, currentYear) << " years to graduate.\n";