Check out example codes for "how to declare a function in c++". It will help you in understanding the concepts better.

Code Example 1

// function example
#include <iostream>
using namespace std;

int addition (int a, int b)
  int r;
  return r;

Code Example 2

#include <iostream>
#include <stdlib.h>
#include <iomanip>
#include <fstream>
using namespace std;

void function_one(double, double, double);

int main() {
  double r1 = 1.0;
  double r2 = 2.0;
  double x = 0.0;
  function_one(r1, r2, x);
  return 0;

void function_one(double rmin, double rmax, double x0) {
  cout << "Function got called" << endl;

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