嵌套For循环到Do while循环

Question

Hi I read the guidelines about homework questions and it says to clearly state that it is homework. This is homework, I have spent the last 45 minutes trying over and over again. I've hit a wall and need help.

My assignment was to take this code that came from a double For loop and convert it into a while loop nested into a for loop. I have successfully completed that. However, the 3rd part is to take that code and make the outer for loop into a do while loop. The output needs to increment a "#" each line like so if the input was "4"

#
##
###
####

Below is my code that I wrote that I need to make the outer for loop into a do while loop:

int main()
{
    int side;

    cout << "Enter a number: ";
    cin >> side;

    for (int i = 0; i < side; i++)
    {
        int j = i;
        while(j >= 0)
        {
            cout << "#";
            j--;
        }
        cout << "\n";
    }
}

This is my attempt so far:

int main()
{
    int side;
    int i;

    cout << "Enter a number: ";
    cin >> side;
    int j=side;
    do
    {
        while(j >= 0)
        {
            cout << "#";
            j--;
        }
        cout << "\n";
        i++;
    }
    while(j >= side);
}

My teacher said as long as the code is explained and I understand how it works that it's okay. Any help would be much appreciated. Thanks.

Answer 1

I suggest

int main()
{
    int side;
    int i = 0;
    cout << "Enter a number: ";
    cin >> side;

    do
    {
        int j = i;
        while(j >= 0)
        {
           cout << "#";
           j--;
        }
        cout << "\n";
        i++;
    }while(i < side)
}

A for loop usually consists in an initialization ( i=0 ), a stop condition ( i < side ) and an increment ( i++ ); why would you not use i anymore?

Answer 2

The first mistake you made is this:

int i; //not initialized!
/*...*/
i++;

and you didn't even use it in your do-while condition.

So while(j >= side); > while (i >= side);

Actually, that's not true, either. Since side is the input, you want i to check if it's smaller not greater then the input. So it's while (i < side);

Another thing is int j=side; , when you decrement j it will never reset, so you must set this into your do-while loop and also initialize it with i rather than side....

Anyway, here's the full code:

#include <iostream>
using namespace std;

int main()
{
    int side;
    int i = 0;

    cout << "Enter a number: ";
    cin >> side;
    do
    {
        int j = i;
        while (j >= 0)
        {
            cout << "#";
            j--;
        }
        cout << "\n";
        i++;
    } while (i < side);

    return 0;
}

example output:

Enter a number: 10
#
##
###
####
#####
######
#######
########
#########
##########

Answer 3

• while(j >= side); should be while(i <= side);
• j should be initialized in each iteration of the outer loop ( j = i; )
• int j=side; is unnecessary.

An friendly suggestion - name your variables and functions descriptively - row and column are much better than i and j .

Answer 4

They answer above solves your problem but let me show you a shorter way to do things:

int main()
{
    int side;

    std::cout << "Enter a number: ";
    std::cin >> side;

    int row = 1;
    do
    {
        int col = 0;
        while (col++ != row)
        {
            std::cout << "#";
        }
        std::cout << "\n";
    } while (row++ != side); //This way, the condition is checked (row != side), and then row is incremented
}