C++ Notes: Summary: Program Structure

Small programs

A common structure for simple, one file, C++ programs:
  1. Comments describing program, author, ...
  2. Include statements specify the header files for libraries.
  3. Using namespace statement. Typically this is only using namespace std;
  4. Global declarations (consts, types, variables, ...). Avoid global variables if possible.
  5. Function prototypes (declarations).
  6. Main function definition.
  7. Function definitions.

Example of main program

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// program-structure/ulam.cpp - Read number, print its Ulam sequence.
// Michael Maus, 2004-10-26

//========================================================= includes
#include <iostream>
using namespace std;

//======================================================= prototypes
int nextUlam(int x);


//============================================================= main
int main() {
    int n;   // Ulam sequence start
    cout << "Enter an integer to see its Ulam sequence." << endl;
    while (cin >> n) {
        cout << "Ulam sequence for " << n << " is " << n;
        while (n > 1) {
            n = nextUlam(n);
            cout << " " << n;
        }
	    cout << endl;
    }
    return 0;
}


//========================================================= nextUlam
int nextUlam(int x) {
    int result;
    if (x%2 == 0) {     // if even
        result = x / 2;
    } else {            // if odd
        result = 3*x + 1;
    }
    return result;
}

Larger program structure

A program that defines classes or numerous methods is divided into many source files. To pass common definitions between these files, header files are created which contain declarations.

Copyleft 2004 Fred Swartz MIT License