Core Concepts of Computer Programming

updated July 31, 2024

TOC

1. Intro
2. Input / Output
   1. Hello World Program
3. Variables & Data Types
   1. Sample Program for Variables and Data Types
4. Operators
   1. Assignment Operators Sample Program
   2. Arithmetic Operators Sample Program
   3. Comparison Operators Sample Program
5. Conditionals
   1. Sample Program Using IF
   2. Sample Program Using IF/ELSE
6. Loops
   1. Sample Program Using Loops
7. Functions
   1. Sample Program Creating And Using Functions
8. More Of My Content

Intro

Of all the inventions in the field of electronics like the radio and telephone, the programmable computer was the most significant one. It changed the world forever.

If a certain device can be programmed the way we want it to behave, then we can simply instruct it to do things for us. That's very practical, isn't it?

After programmable computers, the next big question was how humans would program them. They began developing programming languages and the 1970s was a very remarkable period: the C language was invented.

After this success, great potential was unleashed, and we are now seeing what a programmable computer can do: the era of information, real-time data, almost realistic 3D games, artificial intelligence, etc.

Learning computer science today, unlike in the past, involves many specialized fields, even in software development alone.

And if you are a beginner, you might be discouraged from all the things you need to learn but don't worry: you don't need to learn them all. What you need to learn first is understanding how computers work and the fundamentals of computer programming that all computer programming languages have in common.

And since almost every programming language nowadays directly and indirectly inherits concepts from the C language, we'll be using it to demonstrate the core concepts of programming.

Take note: we don't want to discuss every detail of the code in terms of the C language, rather we just want to get the core concepts of computer programming that are common in different programming languages.

Input And Output

As was mentioned, a programmable computer is very important, but the way you interact with the computer is through input and output: you, as the user, will provide input, the computer will process it (the way it is processed is also programmed), then the computer will output something. The very first demonstration is the "Hello World" program. The programmer will tell the computer to simply display the message on the screen.

But of course, complex programs are not as straightforward as that. Typical programs like binary to human language (and vice versa) takes a lot of processing, an operating system to recognize computer applications, a business collaborative tool with many features to manage data, a 3D game that is almost realistic, an Artificial Intelligence program that can simulate humans in the virtual world!

But of all the things programmers can do, the computer only processes input as binary data (0s and 1s), and it should not be interpreted literally. It's just a representation of something a computer can recognize: the absence or presence of an electric pulse. Compare this with any drawing that can be accomplished just by simply using a dot-and-no-dot pattern! It's the same thing for the computer.

Hello World Program

#include <stdio.h>

int main() {

    printf("Hello World!\n");
    printf("Life is a blessing!\n");

    return 0;

}

In this small program, the #include tells the computer to include a certain source which is needed because it contains the predefined command printf. printf simply tells the computer to display the text provided by the programmer.

As simple as that, you now have the complete idea of what a programmable computer is all about. It's you telling the computer to do things it can handle in terms of binary data.

Variables And Data Types

In computer programming, a variable is just like a container to store digital data. A data type is the way you tell the computer how that data will be interpreted. Should the computer interpret that as letters? or numbers? or words? or simply raw binary data? The computer does not know that, you must tell it exactly.

In computer programming, both these things will enable you to store data and tell the computer what kind of data it is. When you store, you want to retrieve it later as needed. Remember also, computer's memory is different from storage. Think of it as the short-term memory and the storage (the hard disk) as the long-term memory. But during the runtime of a program you are developing, you refer to memory as storage. The computer's memory has full access to the CPU while the disk does not have that access. In order to read contents from the hard disk, a request should be made. Hence, in programming, you are using the memory first, not the disk. There is current development to combine the two, but it is still ongoing.

Take note, the details of memory, hard disk, and CPU are quite complex, but the mentioned details above will serve as the starting point for full comprehension.

Sample Program for Variables and Data Types

#include <stdio.h>

int main() {

    int i = 1;
    char myletter[] = "myletter";
    float x = 1.23;

    printf("int i: %d\n", i);
    printf("char myletter[]: %s\n", myletter);
    printf("float x: %f\n", x);

    return 0;
}

In this simple program, we declare and assign three variables with different data types:

1. an integer variable i that contains the numeric value 1
2. a character array myletter[] that contains the string "myletter"
3. a float variable x that contains the value 1.23

After that, the program instructs the computer to display these values.

Operators

In programming, just like in mathematics, there are operators. The most common in computer programming are assignment, arithmetic, and comparison operators.

Assignment Operators Sample Program

#include <stdio.h>

int main() {
    int c;

    c = 10;
    printf("c = %d\n", c);
    c = 15;
    printf("c = %d\n", c);
    c = 3;
    printf("c = %d\n", c);

    return 0;
}

The most common assignment operator is =. It should not be confused with the double == comparison operator.

In this example, the = operator is simply assigning a value to a variable. The result is:

c = 10
c = 15
c = 3

Variable c contains a value at a specific time. It was changed in the program three times.

Arithmetic Operators Sample Program

#include <stdio.h>

int main() {
    int a = 10;
    int b = 5;
    int result;

    printf("where a = %d & b = %d\n", a, b);

    result = a + b;
    printf("a + b = %d\n", result);
    result = a - b;
    printf("a - b = %d\n", result);
    result = a * b;
    printf("a * b = %d\n", result);
    result = a / b;
    printf("a / b = %d\n", result);

    return 0;
}

Since these are arithmetic operators, they will perform basic arithmetic operations.

The result is:

where a = 10 & b = 5
a + b = 15
a - b = 5
a * b = 50
a / b = 2

Comparison Operators Sample Program

#include <stdio.h>

int main() {
    int a = 10, b = 10, c = 20;

    printf("%d == %d is %d\n", a, b, a == b);
    printf("%d == %d is %d\n", a, c, a == c);
    printf("%d > %d is %d\n", a, b, a > b);

    return 0;
}

Since these are comparison operators, they compare the left and right side values.

The result is:

10 == 10 is 1
10 == 20 is 0
10 > 10 is 0

The result is either 0 or 1. Remember, 0 is FALSE and 1 is TRUE.

Conditionals

In a comprehensive program, the computer must make decisions based on given conditions. Of course, the computer cannot do this alone; you must instruct it exactly. The most common conditional statement is the IF statement, often extended with IF/ELSE.

Sample Program Using IF

#include <stdio.h>

int main() {
    int i = 10;

    if (i == 10) {
        printf("Expected value is the same as variable i, so the result is TRUE.\n");
    }

    return 0;
}

In a single IF statement, the programmer wants to test, expect, or verify something. In this program, the programmer expects that the variable i has the value 10. Since variable i does have the value 10, the statement Expected value is the same as variable i, so the result is TRUE. will be printed. If the expected value is not the same as the value of the variable, the statement will not be printed.

Sometimes, just an IF statement is not sufficient, particularly when you want to handle the FALSE result or create a nested IF-ELSE. In such cases, you extend it to catch the FALSE result.

Sample Program Using IF ELSE

#include <stdio.h>

int main() {
    int i = 10;

    if (i == 11) {
        printf("Expected value is the same as variable i, so the result is TRUE.\n");
    } else {
        printf("Expected value is not the same as variable i, so the result is FALSE.\n");
    }

    return 0;
}

Not only can the statement in the ELSE branch be printed, but you can also perform various actions such as correcting an error, navigating to a certain part of a program, etc. That's the power of catching the FALSE result.

Loops

There are commands or portions of your program to be repeated several times. Loops are there to do that. Now, there are simple loops and loops based on a given condition, much like a repeated IF statement. Simple loops are like "repeat 10 times" or "repeat forever." Conditional loops are loops with specific conditions other than simple iteration, just like in robot programming: "repeat until color red," "repeat until the distance is less than 50mm," etc.

The most common loops that we see in computer programming are the for loop, while loop, and do-while loop.

Sample Program Using Loops

#include <stdio.h>

int main() {
    int n = 11;
    int i;
    int x[n];

    printf("The `for` loop:\n");
    for (i = 1; i < n; i++) {
        printf("Iteration: %d | Hello World.\n", i);
    }

    int y = 0;
    printf("------\n");
    printf("The `while` loop:\n");
    while (y < 10) {
        y += 1;
        printf("Iteration: %d | Hello World.\n", y);
    }

    y = 0;
    printf("------\n");
    printf("The `do-while` loop:\n");
    do {
        y += 1;
        printf("Iteration: %d | Hello World.\n", y);
    } while (y < 10);

    return 0;
}

The result:

The `for` loop:
Iteration: 1 | Hello World.
Iteration: 2 | Hello World.
Iteration: 3 | Hello World.
Iteration: 4 | Hello World.
Iteration: 5 | Hello World.
Iteration: 6 | Hello World.
Iteration: 7 | Hello World.
Iteration: 8 | Hello World.
Iteration: 9 | Hello World.
Iteration: 10 | Hello World.
------
The `while` loop:
Iteration: 1 | Hello World.
Iteration: 2 | Hello World.
Iteration: 3 | Hello World.
Iteration: 4 | Hello World.
Iteration: 5 | Hello World.
Iteration: 6 | Hello World.
Iteration: 7 | Hello World.
Iteration: 8 | Hello World.
Iteration: 9 | Hello World.
Iteration: 10 | Hello World.
------
The `do-while` loop:
Iteration: 1 | Hello World.
Iteration: 2 | Hello World.
Iteration: 3 | Hello World.
Iteration: 4 | Hello World.
Iteration: 5 | Hello World.
Iteration: 6 | Hello World.
Iteration: 7 | Hello World.
Iteration: 8 | Hello World.
Iteration: 9 | Hello World.
Iteration: 10 | Hello World.

As you can see here, it's just printing "Hello World" ten times, whether it's a for loop, while loop, or do-while loop.

Functions

A function is a group of statements (commands) that together perform a task. There are built-in functions and functions that a programmer will create according to his/her needs.

Sample Program Creating And Using Functions

#include <stdio.h>

void myFunction() {
    printf("Hello World.\n");
    printf("Life is beautiful.\n");
    printf("Cherish every single moment.\n");
}

int main() {
    myFunction();
    return 0;
}

The function myFunction() is created by declaring void first. Other functions will return values, but for simplicity, we create a void function. A void function will simply execute the commands contained in it, nothing else.

Then inside the main function, you simply invoke it by its name. All the commands inside that function will be executed line by line.

Why use functions? Imagine if there were none. Complex programs are usually composed of thousands to millions of lines of code. Without any grouping, that would be very hard to handle.

If a function is generic and can be used for other projects, you can simply separate it for distribution. So your code is now reusable.

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