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;
}


Heck yeh! Great work.
I think most critique has been covered.
I consider too-many-indentations to be a code smell.
Not actually an issue, but maybe there is…
There is nothing wrong with your code, and no reason to change it (beyond error catching as you have discovered). It runs, is easy to follow, and doesn’t over-complicate.
I like descriptive function names and early returns (ie, throw or return on all the conditions that means this function shouldn’t continue, then process the parameters to return a result).
This could massively clean up what’s going on.
There could be a “getUserCommand()” that returns the desired number, or 0 if it’s invalid.
If the returned value is 0, then break.
If the returned value is 6, then print values; then break.
Otherwise we know the value should be 1-5.
You could use an Enum to define the choices.
This way, the print lines and the conditional tests can both reference the enum. It also removes “magic numbers” (IE values that appear in code with no explanation).
In something simple like this, it doesn’t really matter. But it improves IDE awareness (helping language servers suggest code/errors/fixes). And Makes the code SOO much more descriptive (Ie “choice == 3” becomes “choice == Choices.Product”).