this post was submitted on 22 Nov 2025
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Programming

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Please excuse - and do not hesitate to point out - any violation against etiquette that I might be committing here... I am new here.

I started to learn C a few months ago as a hobby as part of a bigger project, namely to learn about computers in general. I have had so much fun reading Code - The Hidden Language of Computer Hardware and Software by Charles Petzold. But that's another story...

I was about to buy a few new SSDs and needed to do some budgeting. Instead of using my phone's calculator, I decided to try to write a calculating program in C, because I hadn't touched programming for some weeks or months because life and I wanted to see if my knowledge had matured some.

The goal was to have it do the four standard arithmetics and also save the last result in a variable, which I just called "memory" for lack of bette phrasing on my part. Maybe next week I'll figure out how to make it possible to use the value saved in memory instead of having to type a number.

I welcome any constructive criticism on how and why this code is up to code or not(sorry...), if it can be improved and how or even if it's just garbage and why that is. I am just proud that it worked without gcc throwing any errors.

#include <stdio.h>

int main(void) {

        int num1 = 0;
        int num2 = 0;
        int choice = 0;
        int memory = 0;

        printf("Welcome to the Calculator of the century!\n\n");

        while (1) {
                printf("What would you like to do?\n\n");
                printf("(1) Add two numbers\n(2) Subtract two numbers\n(3) Multiply two numbers\n(4) Divide two numbers\n(5) Show memory\n(6) Exit\n\n");
                printf("Enter 1, 2, 3, 4, 5 or 6: ");
                scanf("%d", &choice);

                if (choice >= 6 || choice < 1) break;

                if (choice == 5) {
                        printf("\n%d in memory.\n\n", memory);
                } else if (choice < 5 || choice > 0) {
                        printf("\nEnter the first number: ");
                        scanf("%d", &num1);
                        printf("Enter the second number: ");
                        scanf("%d", &num2);
                }

                if (choice == 1) {
                        printf("\nThe sum of %d and %d is %d\n\n", num1, num2, num1 + num2);
                        memory = num1 + num2;
                } else if (choice == 2) {
                        printf("\nThe difference of %d and %d is %d\n\n", num1, num2, num1 - num2);
                        memory = num1 - num2;
                } else if (choice == 3) {
                        printf("\nThe product of %d and %d is %d\n\n", num1, num2, num1 * num2);
                        memory = num1 * num2;
                } else if (choice == 4) {
                        printf("\nThe quotient of %d and %d is %d\n\n", num1, num2, num1 / num2);
                        memory = num1 / num2;
                }
        }

        printf("\nWe hope to see you soon again!\n");
        return 0;
}
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[–] ulterno@programming.dev 2 points 3 days ago

If you feel like making a more elaborate thingy, which can take full inputs like "1 + 2" (I know I wanted to, back when I made my first calculator), you can check out this link for starters https://www.calcworld.net/infix-to-postfix-converter/

Except that instead of storing the postfix output in another string (as is done on the website), you want to be segregating each and every value into separate variables (perhaps in an array), while separating the values from the operators.

Once that is done, you can then take the values 1-by-1 and apply the operations.

It becomes fun after that.