Small Steps VIII — Build with Several Files

Give Each File a Job

Pass values to a function and receive its result.

Separate the score calculation

Name files after their jobs. Create a new ScoreCard project. Keep main.cpp, score.h, and score.cpp in the same folder and replace their contents as follows.

score.h

#pragma once

int add_points(int score, int points);

score.cpp

#include "score.h"

int add_points(int score, int points)
{
    return score + points;
}

main.cpp

#include "score.h"

void small_main()
{
    int score = 0;
    score = add_points(score, 10);
    score = add_points(score, 20);
    print(score);
}

Run Project prints 30. main.cpp controls the program's flow; score.cpp handles the calculation. The score is a local variable in main. Passing values in and returning a new value avoids a shared global variable.

Start with a header named after its source file. Put function declarations in the header and definitions in the source. You do not need a separate file for every small function.

Check the behavior in one file

int add_points(int score, int points)
{
    return score + points;
}

void small_main()
{
    int score = 0;
    score = add_points(score, 10);
    score = add_points(score, 20);
    print(score);
}

Exercise — Check it yourself

Add another call worth 5 points to print 35 in the one-file practice. Then add the same call to main.cpp in your project. Do score.h and score.cpp need to change?

int add_points(int score, int points)
{
    return score + points;
}

void small_main()
{
    int score = 0;
    score = add_points(score, 10);
    score = add_points(score, 20);
    print(score);
}

Hint

Use the menus described above. The solution below is for the one-file practice. Apply the same change to the file with that job in your project.

int add_points(int score, int points)
{
    return score + points;
}

void small_main()
{
    int score = 0;
    score = add_points(score, 10);
    score = add_points(score, 20);
    score = add_points(score, 5);
    print(score);
}