simple calculator

main.cc

#include <iostream>
#include <string>

using namespace std;

// Function Declarations
int get_value(string msg);
char get_operator(string msg);
int compute(int lhs, int rhs, char op);

int main()
{
  // Let's call a function to grab a value, and place the returned value
  // into variable a
  int a = get_value("Enter left-hand operand:");

  // Let's call a function to grab the operator, and place the returned value
  // into variable op
  char op = get_operator("Enter operator:");

  // Let's call a function to grab a value, and place the returned value
  // into variable a
  int b = get_value("Enter right-hand operand:");

  // Compute the result of `a op b`
  int result = compute(a,b,op);

  cout << "Result: " << result << endl;
}

// Output a message to user, grab input for stdin
// Assumes that valid input is given
int get_value(string msg) {
  int value = 0;
  cout << msg << endl;
  cin >> value;
  return value;
}

// Output a message to user, grab operator from stdin
// Assumes that valid input is given
char get_operator(string msg) {
  char op;
  cout << msg << endl;
  cin >> op;
  return op;
}

int compute(int a, int b, char op) {
  switch(op) {
  case '+':
    return (a + b);
    break;
  case '-':
    return (a - b);
    break;
  case '*':
    return (a * b);
    break;
  case '/':
    return (a / b);
    break;
  default:
    cout << "invalid operator passed!" << endl;
    return -1;
    break;
  }
}

main2.cc

#include <iostream>

int Integer1();
char Operator();
int Integer2();
int DoMath(int a, char m, int b);
void Display(int result);

int main()
{
  int a = Integer1();

  char m = Operator();

  int b = Integer2();

  int result = DoMath(a, m, b);

  Display(result);
}
int Integer1()
{
  using namespace std;

  cout << "Enter a number" << endl;

  int a;

  cin >> a;

  return a;
}
char Operator()
{
  using namespace std;

  cout << "Enter your operator: +, -, *, or /" << endl;

  char m;

  cin >> m;

  return m;
}
int Integer2()
{
  using namespace std;

  cout << "Enter your next number" << endl;

  int b;

  cin >> b;

  return b;
}
int DoMath(int a, char m, int b)
{
  using namespace std;

  if (m == '+')

    return a + b;

  if (m == '-')

    return a - b;

  if (m ==  '*')

    return a * b;

  if (m == '/')

    return a / b;

  return 0;
}
void Display(int result)
{
  using namespace std;

  cout << "The answer is " << result << endl;
}