How to write a simple C program to check if a number is prime using Visual Studio code.
Tags: c, tutorial, vscode, programming
Published: 2023-12-29 16:05:03

## Introduction

C is a procedural language. it is renowned for its portability, efficiency, and simple syntax.

Visual Studio Code is a development tool. Inbuilt with a code editor that supports development processes and more.

In this article, you’ll learn to write a simple C program to check if a number is prime using Visual Studio Code.

### Prerequisite

- Basic knowledge of C programming and its syntax.


- Visual Studio Code is installed on your machine. Go to the [official website](https://code.visualstudio.com/download) to install it.

### Terminologies to understand to aid with this lesson

- Prime number - This is a number that can only be divided by one and itself, for example, 2, 3, 5, 7… etc.


- Composite number - is a positive integer divided by 1 and other numbers apart from itself, for example, 4, 6, 8, 9… etc.

## Steps

Let’s dive in by breaking down the processes involved in this article.

### Step 1 - Download Extensions

Extensions are software that extends and enhances the functionality of the editor.

Launch Visual Studio Code and click on **Extensions**. It can also be accessed using the shortcut keys `ctrl`+`shift`+X or the `command` key for MAC. Install the following extensions:

1. **C/C++ Extension Pack:**

The **C/C++ Extension Pack** provides a comprehensive development environment for C and C++ programming in Visual Studio Code. This extension pack includes essential tools, language support, debugging capabilities, and extra features tailored for C and C++ development.

![An image of C/C++ Extension Pack installation](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/s7m826pfjauzau3dydi8.png)

2. **C/C++ Extension:**

The **C/C++** extension is a core component within the extension pack. It focuses on providing language support for C and C++ in Visual Studio Code. This includes features such as syntax highlighting, code suggestions, debugging support, etc.

![An image of C/C++ extension installation](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/mfroxf09letprwb01ed6.png)

3. **Code Runner:**

The **Code Runner** extension is a tool that allows the execution of code snippets or entire files

![An image of Code Runner extension installation](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/nggpfgwncpao2dzpkwzl.png)

#### Step 1.1 - Change Settings

Click the gear icon on the bottom-left corner of your screen and click on **Settings**. Or, use the shortcut keys `ctrl`+`,`, the `command` key for Mac.


![An image of the gear icon and Settings](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/9ptawibo5z85m0nk5tgq.png)


Next, enable the **Code-runner: Run In Terminal** feature.

Input **“run code in terminal”** in the search bar and check the **Code-runner: Run In Terminal** checkbox.


![An image of the input “run code in terminal” in the search bar](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/olxgy8gyj3gxp2ugvrlt.png)
The **Code-runner: Run In Terminal** feature allows user input in the terminal. In this lesson, user input handling is required. i.e. if your code prompts for user input, you can provide it within the terminal.

### Step 2 - Open a folder

A folder has many uses such as file organization, namespace management, etc.

Navigate the Explorer tab or use the shortcut keys `ctrl`+`shift`+`E`, the `command` key on Mac.

Click **Open Folder** and proceed to create a new folder on your file explorer/manager.


![An image of Open Folder](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/dezn060b54fxfwvn73vf.png)

Name the folder whatever you want or you can name it “C”. Click Select Folder after.


![An image of New Folder and Select Folder](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/3mq74zijkwqat0ehh9g7.png)

#### Step 2.1 - Create a file

A file serves many functions, in this lesson, you’ll be storing your source code in a file.

Click on your folder, and beside it, three icons will appear, click the **New File** icon.


![An image of the New File icon](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/0jpl5pmwqfkc245rm2js.png)

Name your file with the `.c` extension to specify the C source code. Click enter to save the file.


![An image of a file with the .c extension](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/yu14t6pm8hwacjgch55h.png)

### Step 3 - Code

Your workspace is set up, Next, you’ll write your code to check if a number is prime. In your editor, follow the steps below:

#### Step 3.1 - Header file

Include the standard input/output and math libraries.

```
#include <stdio.h>
#include <math.h>
```
`#include <stdio.h>` includes the standard input/output library. This library is used for input/output operations.

`#include <math.h>` includes the math library. This library is used for mathematical functions.

#### Step 3.2 - Entry point

Include the `int main()` function.

```
#include <stdio.h>
#include <math.h>

int main()
{
    
}
```
The int main function is the entry point, it returns an integer value(often 0) to state success. An entry point is where program execution starts.

#### Step 3.3 - Declare variables and user input

Declare Variables:

```
#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
}
```
`int number` stores the user input. While `int i, value1, value2, count = 0;` declare variables for loop control, intermediate values, and a counter.

Next, add code to accept user input:

```
#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);
}
```
`printf("Enter a number: ")` prompts the user to enter a number. `scanf("%d", &number);` reads the user input and stores it.

#### Step 3.4 - Find the square root

```
#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);

    value1 = ceil(sqrt(number));
    value2 = number;
}
```
`value1 = ceil(sqrt(number));` calculates the square root of `number` using the `sqrt` function. The `ceil` function approximates the square root to the nearest integer.

`value2 = number` is initialized to the value of `number`. This will be used in later calculations or conditions. i.e. the prime number checking logic.

#### Step 3.5 - Loop iteration

```
#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);

    value1 = ceil(sqrt(number));
    value2 = number;

    for(i = 2; i <= value1; i++)
    {
        if(value2 % i == 0)
            count = 1;
    }
}
```
The loop checks the divisibility of `value2` by `i`. If true, `count` is set to 1, else it remains 0.

#### Step 3.6 - Check if the number is prime

```
#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);

    value1 = ceil(sqrt(number));
    value2 = number;

    for(i = 2; i <= value1; i++)
    {
        if(value2 % i == 0)
            count = 1;
    }
    if((count == 0 && value2 != 1) || value2 == 2 || value2 == 3)
    {
        printf("%d is a prime number", value2);
    }
    else
    { 
        printf("%d is not prime number", value2);
    }
    return 0;
}
```
The `if` statement checks if the number is prime. If the conditions are true, it prints the number is a prime number, if false, it prints it is not a prime number. `return 0` indicates the program has been executed successfully.

### Step 4 - Run Code

To run your code, click on the **Run Code** icon on the top-left corner of your screen(first icon). Or use the shortcut keys `ctrl`+`alt`+`N`, the `command` key on Mac.

### Step 5 - Terminal Input

After clicking the **Run Code** icon, the terminal will appear at the bottom of your screen. You will see a prompt that says “Enter a number” on the terminal. Please input a number in the terminal when prompted.

If the number is prime, the output below is displayed;

![An image of the terminal](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/m8ilje5l6dutg3t6hvci.png)

Otherwise, this output below is displayed;

![An image of the terminal](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/lgpthhjbwiu3hjrzc205.png)

## Conclusion

In this tutorial article, you wrote a C program to check if a number is prime. Also leveraging the capabilities of Visual Studio code as a powerful integrated development environment(IDE). You covered inputs, loops, and math functions. All basics for a solid foundation in C programming.

If you enjoyed this tutorial and would like to learn more on this blog, feel free to follow, comment, and leave claps. Happy Coding!

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