如何在 C++ 中将每个打印行增加到 2 的 n 和 n-1 的幂？

Question

Trying to write a program in C++ that prints rows of "*" based on the result of 2^n then after a certain number is entered decrease 2^n-1. For example any where between 0 and 6 (both of these being n) a row of stars is printed from *, **, **** and so forth. Then anything between 7 and 12 the number of stars decreases 2^n-1.

So far I have this but it only prints one singe line of * based on the result of the exponent.

int base = 2, exponent, result;
    char star = '*';

    cout << "Enter a number between 0 and 12:  ";
    cin >> exponent;

    result = pow(base, exponent);
    string pattern = string(result, star);
    cout << pattern << endl;

If user enters 4 
Output; ********

Goal for it to look like this

2^0 = *
2^1 = **
2^2 = ****
2^3 = ********
2^4 = ****************
2^5 = ********
2^6 = ****
2^7 = **
2^8 = *

Hope that makes sense.

Answer 1

Right now you are taking the input and storing it in your exponent variable, and then only printing once.

What you want to do is create a loop that varies your exponent up to maximum value based on the input you got.

ie for the increasing part

int max_num;
cin >> max_num 
for (int i; i < max_num; i++){
   // code to print 2^n stars, with n=i 
}

You can write a similar loop for the decreasing part by counting down.

int max_num;
cin >> max_num 
for (int i; i >= 0; i--){
   // code to print 2^n stars, with n=i 
}

Answer 2

Sorry i needed to edit your code. you have to use iteration for you to achieve that output.

    int rvalue = 1;
    int i;
    string outputDisplay = "";

    int base_ = 2;
    int exponent = 0;
    cout << "Enter a number between 0 and 12:  ";
    cin >> exponent;



    for (i = 1; i <= exponent; i++)
        rvalue = rvalue * base_;

    while (rvalue != 0)
    {
        outputDisplay += "*";
        rvalue--;
    }
    cout << outputDisplay << endl;

On this part im getting the X^n output without using any library (Math.Pow for example).

  for (i = 1; i <= exponent; i++)
            rvalue = rvalue * base_;

For the output you just need to add "*" on a string depending on the rvalue or the X^n value.

 while (rvalue != 0)
        {
            outputDisplay += "*";
            rvalue--;
        }

On this case i inputted 2 and 4 initially on the variable, output will be like;

Another run;

Answer 3

Ok so the problem is that you need a loop, i tried to not edit your variables this is the best i could do:

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    int base = 2, exponent, result;
    char star = '*';
    int aux=1;
    cout << "Enter a number between 0 and 12:  ";
    cin >> exponent;
    for(int i=0;i<=exponent;i++)
    {
        cout <<" 2 ^ "<<i<<" = ";
        result = pow(base, i);
        for(int j=1;j<=result;j++)
        {
            cout<<star;
        }
        cout<<endl;
    }
    aux=exponent;
    for(int i=exponent-1;i>=0;i--)
    {
        cout <<" 2 ^ "<<aux<<" = ";
        aux++;
        result = pow(base, i);
        for(int j=1;j<=result;j++)
        {
            cout<<star;
        }
        cout<<endl;
    }
    return 0;
}

the first for loop is when the numbers are under the exponent and the other are for when the numbers are above the exponent. Hope that helps you, i will provide further help if needed!

This is the photo of the run window click to see image