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 Here's an example: #include <iostream> using namespace std; // function to calculate volume of a cube double cubeVolume(double side = 1.0) {     return side * side * side; } int main() {     double side1 = 3.0; // side of cube 1     double side2 = 4.0; // side of cube 2     double side3 = 5.0; // side of cube 3          // calculate volumes of cubes using default argument     double volume1 = cubeVolume(); // default side = 1.0     double volume2 = cubeVolume(side1);     double volume3 = cubeVolume(side2);     double volume4 = cubeVolume(side3);          // display volumes of cubes     cout << "Volume of cube with side " << side1 << " is " << volume2 << endl;     cout << "Volume of cube with side " << side2 << " is " << volume3 << endl;     cout << "Vol...