Write a program that prints all possible combinations of single-digit numbers

Using both putchar and printf functions with for and while loops

UpdatedOctober 19, 2023

Write a program that prints all possible combinations of single-digit numbers

Heya! 👋 I love helping people, and one of the best ways I do this is by sharing my knowledge and experiences. My journey reflects the power of growth and transformation, and I’m here to document and share it with you.

I started as a pharmacist, practicing at a tertiary hospital in the Northern Region of Ghana. There, I saw firsthand the challenges in healthcare delivery and became fascinated by how technology could offer solutions. This sparked my interest in digital health, a field I believe holds the key to revolutionizing healthcare.

Determined to contribute, I taught myself programming, mastering tools like HTML, CSS, JavaScript, React, PHP, and more. But I craved deeper knowledge and practical experience. That’s when I joined the ALX Software Engineering program, which became a turning point. Spending over 70 hours a week learning, coding, and collaborating, I transitioned fully into tech.

Today, I am a Software Engineer and Digital Health Solutions Architect, building and contributing to innovative digital health solutions. I combine my healthcare expertise with technical skills to create impactful tools that solve real-world problems in health delivery.

Imposter syndrome has been part of my journey, but I’ve learned to embrace it as a sign of growth. Livestreaming my learning process, receiving feedback, and building in public have been crucial in overcoming self-doubt. Each experience has strengthened my belief in showing up, staying consistent, and growing through challenges.

Through this platform, I document my lessons, challenges, and successes to inspire and guide others—whether you’re transitioning careers, exploring digital health, or diving into software development.

I believe in accountability and the value of shared growth. Your feedback keeps me grounded and motivated to continue this journey. Let’s connect, learn, and grow together! 🚀

Comments (1)

Join the discussion

Oluwademilade Eniade3y ago

Hi, Nice presentation Dr Obed 👍 What if you wanted to print up to 20 I've tried out your code but I could only get 1 to 9..after which I got :;<.....

C Programming

Part 9 of 40

From today, I will be starting lessons on C programming in my ALX Software Engineering class and I look forward to sharing with you everything I learn through this series.

Up next

Write a program in C that prints the first 50 Fibonacci numbers, starting with 1 and 2

To be able to answer this question, you need to understand what a fibonacci number is and how to derive a fibonacci sequence. A fibnonacci number is any number in a sequence which happens to be the sum of the two preceeding numbers. This means that t...

More from this blog

Choosing the Right AI Model for the Job

Imagine you have access to several AI models. One is extremely powerful but expensive. Another is fast and cheap but less capable. A third is excellent at coding but weaker at reasoning. Which on

Jun 16, 202610 min read

How Source Documents Make AI More Reliable

In the last lesson, you learned something important: AI can generate information that sounds convincing while still being completely wrong. That happens because AI primarily predicts patterns in langu

Jun 2, 20268 min read

Why AI Sounds Smart Even When It Is Wrong

One of the strangest things about modern AI is this: It can sound extremely intelligent while still being completely wrong. That is what makes AI both impressive and dangerous at the same time. You

Jun 2, 20269 min read

Prompt Engineering: Thinking Like a Professional AI User

At this point, you already understand something many AI users never fully realize: AI does not read prompts like humans do. It processes: tokens patterns structure and attention distribution Tha

May 30, 20268 min read

How AI actually processes your prompt under the hood

One of the biggest mistakes people make when using AI is assuming the AI reads like a human. It does not. Humans: infer meaning read between the lines fill in missing context guess intentions AI

May 30, 20268 min read

Dr. Ehoneah Obed

86 posts

Software engineer writing about systems: in code, in learning, in life. I reverse-engineer complex problems into frameworks. Pharmacist → SWE → Founder.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9

The question is about writing a C program that produces the outcome above.

There are several ways we can have a program to print all the possible combinations of single-digit numbers. In this tutorial, we will look at how to use:

putchar
printf

Also, for each of them, we can look at multiple ways of achieving the expected outcome. In this tutorial we will take a look at how to use two different types of loops to achieve the result;

For loop
While loop

Using `putchar` to print all combinations of single-digit numbers

First we will look at how to do that with a for loop and afterwards implement the same code using a while loop.

By default, the putchar function is used for displaying single characters to the screen, but we need to make it print integers this time round.

What can help us here is the fact that the putchar function recognizes ASCII codes and is able to print the corresponding integer value of any ASCII code. This means we would also need to know the ASCII codes for the digits (0, 1, 2...9).

ASCII Code	Interger Value
048	0
049	1
050	2
051	3
052	4
053	5
054	6
055	7
056	8
057	9

With a `for` loop

#include <stdio.h>

/**
 * main - main block
 * Description: Print all possible combinations of single-digit numbers.
 * Numbers must be separated by commas and a space.
 * You can only use `putchar` to print to the console.
 * You can only use `putchar` up to four times.
 * You are not allowed to use any variable of type `char`.
 * Return: 0
 */

int main(void)
{
    int x;

    for (x = 48; x < 58; x++)
    {
        putchar(x);
        if (x < 57)
        {
            putchar(44);
            putchar(32);
        }
    }
    putchar('\n');
    return (0);
}

If you don't know the ASCII codes and would still want to use the putchar function, there is a way around it.

You can forcefully convert an integer to a character inside the putchar function. This can be done by adding '0' to the integer.

The above code can therefore be re-written as:

#include <stdio.h>

int main(void)
{
    int x;

    for (x = 0; x < 10; x++)
    {
        putchar(x + '0');
        if (x < 9)
        {
            putchar(',');
            putchar(' ');
        }
    }
    putchar('\n');
    return (0);
}

With a `while` loop

Let's use the while loop to answer the tasks in the same way we did for the for loop.

Using the ASCII codes

#include <stdio.h>

int main(void)
{
    int x = 48;

    while (x < 58)
    {
        putchar(x);
        if (x < 57)
        {
            putchar(44);
            putchar(32);
        }
        x++;
    }
    putchar('\n');

    return (0);
}

Converting integers to characters with the putchar

#include <stdio.h>

int main(void)
{
    int x = 0;

    while (x < 10)
    {
        putchar(x + '0');
        if (x < 9)
        {
            putchar(',');
            putchar(' ');
        }
        x++;
    }
    putchar('\n');

    return (0);
}

Using `printf` to print all combinations of single-digit numbers

With a while loop

#include <stdio.h>

int main(void)
{
    int x = 0;

    while (x < 10)
    {
        printf("%d", x);
        if (x < 9)
        {
            printf(", ");
        }
        x++;
    }
    printf("\n");

    return (0);
}

With a for loop

#include <stdio.h>

int main(void)
{
    int x;

    for (x = 0; x < 10; x++)
    {
        printf("%d", x);
        if (x < 9)
        {
            printf(", ");
        }
    }
    printf("\n");

    return (0);
}

The outcome for all the above codes are:

0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Command Palette

Comments (1)

C Programming

Write a program in C that prints the first 50 Fibonacci numbers, starting with 1 and 2

More from this blog

Using putchar to print all combinations of single-digit numbers

With a for loop

With a while loop

Using printf to print all combinations of single-digit numbers

Using `putchar` to print all combinations of single-digit numbers

With a `for` loop

With a `while` loop

Using `printf` to print all combinations of single-digit numbers