Working with files & FOR loop [closed] - c++

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My task is: in every language is n most used words. A boy after d days is leaving for Sweden. Wanting to understand Swedish, the first day he learns z words and the each following day k words more than a day before. Write a program, which would check if a boy will successfully will learn n words during d days.
Let's say that he needs to learn 100 words. He has 20 days. The first day he learned 5 words. Each following day he learned 1 words more than a day before.
In this case answer should be: yes (he will successfully will learn it during 20 days), and 11 (during 11 days he will learn 100 words).
I have a code written.
#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;
int main()
{
int n, d=0, k, z;
ofstream fr("Rezults.txt");
ifstream fd("Data.txt");
fd>>n>>d>>z>>k;
int learned_words = 0;
for(int i=0; i<d; i++){
learned_words += z;
z = z+k;
}
if(n<=learned_words) {
fr<<"Yes"<<endl;
}
else
{
fr<<"No"<<endl;
}
z=z-d; d=0;
for(int m=0; m<=n; m+=z, z+=k, d++) {}
cout << "You need " << d << " days to learn " << n << " words";
fd.close();
fr<<d;
fr.close();
return 0;
}

Answer 1

You can simply count the loop by using the for loop in this way:
for (i=z; i<=n; i++)
{
}
cout<< i << endl;
You can simply see the variable "i"'s value right after the loop

Answer 2

This simple function solves the problem in the beginning of your question:
// z : the number of words learned during the first day
// k : this much more we learn after every day
// (i.e first day we learn z words, then z+k, then z+k+k etc.)
// d : this many days we have time to learn
// n: this many words we should learn
bool solve(int z, int d, int k, int n) {
int learned_words = 0;
for(int i=0; i<d; i++){
learned_words += z;
z = z+k;
}
if(n<=learned_words) {
return true;
}
return false;
}
To answer your question about loops, I think the following very simple loop would work:
int n = 100;
int z = 5;
int k = 1;
int d = 0;
for(int m=0; m<n; m+=z, z+=k, d++) {}
cout << "You need " << d << " days to learn " << n << " words";
Here the loop will get executed the minimal number of times needed to learn those n words. The variable d counts the days needed and must be declared before the loop. m counts how many words we have learned.

Answer 3

Despite having for loop in the title, there's no requirement for the loop in the task and no reason to actually use it here (unless you're limited to integer arithmetic).
It would be much easier to simply compute days needed to learn n words (it's simple quadratic equation) and compare it with d.
Number of words (y) learnt during first x days is:
y = z * x + k * x * (x-1)/2. So just solve this equation for y = n.
I'd do something like: (variables a and b are coefficients of the quadratic equation).
const double a = k/2.0;
const double b = z-k/2.0;
const double days_needed = -b + ::sqrt(b*b + 4 * a * n)/(2.0 * a);
std::cout << (days_needed <= d ?"yes":"no") << ", you need " << ::ceil(days_needed) << "days\n";