SOLVED: What does type A5_C, PA5_C, and Pc mean?

Lily — Mon, 25 Nov 2019 20:23:33 +0000

UPDATE (Nov 26):
Through more indepth analysis! Finally figured out what it means! At least I hope it's really what it means, but seeing how it trends with other types, I think it's correct!

A5_c - means it's an array of 5 char type elements
PA5_c - means it's a pointer to the array of 5 char type elements
Pc - means pointer that holds an address to another variable

Praise God!

Hello everyone!
I recently started to learn cpp on my own and is learning the concept of pointers, which I hear is a very challenging concept, so I wanted to practice until I fully understand it. The part I am on is about arrays and pointers and through using the mac terminal and the GNU compiler, I wrote a simple program like this and also the results can be found in the comments, could someone help me understand what A5_C, PA5_C, and Pc mean? And also please correct me if anything i thought i understood is incorrect :). Thank you in advance!

#include <iostream>
#include <string.h>
#include <typeinfo>

int main() {

char name[] = "Lily";

//prints size of char array which is 5 bytes in this case
std::cout << sizeof(name) << std::endl;

//------------------------------------------------------
//this prints Lily which is of type: A5_C (huh?????????)
std::cout << name << " which is of type: " << typeid(name).name() << std::endl;

//------------------------------------------------------
//this prints 0x7ffee6425b07 which is of type PA5_C 
//(is PA5_C meaning address?)

std::cout << &name << " which is of type: " << typeid(&name).name() << std::endl;

//------------------------------------------------------
//this prints L which is of type c
//which I understand because it's dereferencing the pointer 
//and getting me the content that's occupying the address

std::cout << *name << " which is of type: " << typeid(*name).name() << std::endl;

//------------------------------------------------------
//this prints ily which is of type Pc
//I am assuming this means pointer type but
//then why is it significantly more different than type of name?

std::cout << (name+1) << " which is of type " << typeid(name+1).name() << std::endl;

//------------------------------------------------------
//this prints i which is of type c
//which makes sense, because you can do
//arithmetics with pointer variables and this adds 
//1 byte to name so it gives me 
//the value in the address 1 unit above

std::cout << *(name+1) << " which is of type " << typeid(*(name+1)).name() << std::endl;

//------------------------------------------------------
//this prints _blank which is of type c 
//and makes sense but it's very bad because 
//c++ have no bounds checking for arrays and 
//so this address might store some garbage value

std::cout << *(name+5) << " which is of type " << typeid(*(name+5)).name() << std::endl;

return 0;

}

Please excuse the messy commenting, but hopefully it's clear!!

Resource recommendation to help with deriving mathematical formulas

Lily — Sun, 17 Nov 2019 01:00:39 +0000

Hi everyone,
I am a newbie to software development and lately I've been trying to improve on my problem solving skills and one common theme that stood out to me was my inability to derive mathematical formulas that will help with my programming logic. I am not sure if this makes sense, but let me give you a few examples, and hoping to get some feedback on how to improve on this skill?

Problem 1: Multiples of 3 and 5

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.

I wrote the following function to solve it, which still have lots of room for improvement and need to make it DRY, but I was hoping I could come up with a mathematical formula to solve it instead of using brute force.

function sum(number, max) {
let i = 1;
let result = 0;
let sum = 0;

  while (result < max) {

        result = number * i++;

    if(result < max) {
        sum = sum + result;
    }
  }

  return sum;
}   


console.log(sum(3, 1000) + sum(5, 1000));

Problem 2: Calculate sum up to n

Write a function that calculates sum up to n

I didn't write this, but someone wrote a formula for it involving n, and I have no idea how he was able to derive this.

function sum(n) {
  return n * (n+1)/2;
}

which does the same thing as this:

function sum(n) {
let total = 0;
for (let i=0; i <= n; i++) {
   total += i;
}

return total;
}

Hopefully this clearly explains my question and any recommendation would be greatly appreciated!
Thank you,

DEV Community: Lily

SOLVED: What does type A5_C, PA5_C, and Pc mean?

Resource recommendation to help with deriving mathematical formulas

Problem 1: Multiples of 3 and 5

Problem 2: Calculate sum up to n