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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Sr. Software Engineer here!
- Great job initializing your variables. That’s a surprisingly common source of bugs, and with today’s optimizing compilers it’s basically free to define the starting value at the beginning of your function. Don’t worry if you reassign the value later. The compiler will notice and won’t waste any time doing extra setup unless it actually matters.
- Consider providing an error message for invalid inputs. Humans can be boneheaded and not realize they gave an invalid input.
- Your code isn’t commented. I recommend considering adding a few to build good habits early if you think you could comment something helpful for the reader. Code is read far more often than it is written ideally.
- You perform your math operations twice: once in the
printfand again later when you assignmemory. Consider doing the computation just once to avoid repeating yourself to the computer. This habit tends to produce more efficient programs. Just updatememoryfirst and then reference it directly in your call toprintf. This also protects against bugs where the value displayed wasn’t really the value written to memory. - Consider checking for division by zero and provide an error message for the unreasonable request.
- Maybe return a non-zero status if an error occurs.
Nice work!
Thank you! I really appreciate your guidance! It almost feels like you could have experience from teaching or the likes, since you are so good at explaining! Or maybe that just comes with being a senior SE? Either way, thanks again!
You’re kind! I enjoy reviewing and talking about code. Anytime.
Signing off now, but I did have the strength left to do this:
else if (choice == 4) { if (num2 == 0) printf("\nhttps://en.wikipedia.org/wiki/Division_by_zero\n\n"); else { memory = num1 / num2; printf("\nThe quotient of %d and %d is %d\n\n", num1, num2, memory); } }Cheers!
All the other tips are great. I would also recommend checking out a switch statement, for example https://www.geeksforgeeks.org/c/c-switch-statement/
This will clean up alot of the else if statements. Also I would work on code to organization. For example you test if the choice is greater than or equal to 6 or less than 1, then if it is equal to 5 then check again if it’s less than 5 and greater than 0. You already did that third check.
If you want to go slightly more advanced I would put the steps to ask for and save the input numbers into a function then just call that function on each of the following choices. Would add a functional call but would remove another if statement. If you name it well it would also help on code readability.
Also if you want to take this farther like taking more than 2 numbers or more than 1 operation (for example 2 + 3 * 4) look into reverse polish notation. Basically it’s how to store the equation to make executing them correctly easier. That might be a little advanced for you at this stage though.
Thanks! I really appreciate the more advanced steps too! Now I have something to do next weekend! :D
Just warning you, the rpn suggestion is pretty complex and would be a complete rewrite. You are on chapter 2, rpn would probably be covered in the second book.
Look into the switch statement instead of the else ifs.
Checking it out now. Thanks!
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”).Code by Charles Petzold was formative for me, over 20 years ago. So, excellent choice.
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.
