C++ strings and arrays

Question

I'm Having problems with to of the questions on my C++ homework.

Write a program to analyze gasoline price in the past 10 days. First, ask the user to enter the prices. Then do the following: (a) Calculate and display the average price in the first 5 days and the average price in the second 5 days (b) Compare the two average prices. Determine and report which one is higher (or they are the same). (c) Compare each day’s price (except day 1) with the price the day before. Determine whether it became higher, lower or remained the same. Count and report the number of days the price was higher than, lower than and the same as the price the day before, respectively.

i'm not sure how to compare how to compare the first five days with the last five days, and part c I'm completely lost on....

i'm not looking for someone to do my homework for me, but a push in the right direction would be a great help!

here is what I have made so far:

#include <iostream>
#include <fstream>
using namespace std;


int main()
{
double gasPrice[10];
double firstFive = 0.0;
double lastFive = 0.0;
double ffAvg = 0.0;
double lfAvg = 0.0;

for (int x = 0; x < 10; x = x + 1)
{
    gasPrice[x] = 0.0;
}

cout << "You will be asked to enter daily gas prices for 10 days."<< endl;

 ofstream gasprice;
 gasprice.open("gasprice.txt", ios::app);

 if (gasprice.is_open())
 {
for (int x = 0; x < 10; x = x + 1)
{
    cout << "Enter the gas price " << x+1 << ": ";
    getline(cin, gasPrice[x];
 }




if ( ffAvg > lfAvg)
{
     cout << "The first five days have a lower gas price " << ffAvg << lfAvg << endl;
     }

 else if ( ffAvg < lfAvg)
 {
       cout << "The last five days have a lower gas price " << ffAvg << lfAvg << endl;
     }

 system("pause ");
 return 0;
 }

Homework needs to be tagged as Homework on SO. I re-tagged it for you. — Paul
– Paul, Commented Jul 24, 2011 at 21:32
@PaulPRO: No, it really doesn't, and it really shouldn't. A good question related to one's homework should be indistinguishable from a good question not related to homework. — James McNellis
– James McNellis, Commented Jul 24, 2011 at 21:35
@James McNellis, It's important that people know they are helping with a homework problem so they can help rather than just give the final answer. — Paul
– Paul, Commented Jul 24, 2011 at 21:39
@PaulPRO: That is absolutely wrong (but this is the wrong place to discuss this; this has been discussed many times on meta.stackoverflow.com). — James McNellis
– James McNellis, Commented Jul 24, 2011 at 21:40

Bueller · Accepted Answer · 2011-07-24 21:40:24Z

1

Read the requirements like they are a description rather than a computer formula. It can become overwhelming when learning something for the first time and we get drowned by the things that would come natural in another environment.

Anyway, you are not to compare the days individually but an AVERAGE of the days. So you first need to compute the AVERAGE of the first five and the AVERAGE of the second five days, then compare that.

For the second part of your question, aggregators for your totals is the push I would give you.

Hope this helps.

answered Jul 24, 2011 at 21:40

Bueller

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Comments

Thomas Russell · Accepted Answer · 2011-07-24 21:41:23Z

Break down the problem in to a series of stages: Firstly, you need to get 10 input prices from the user, and store them in an array of size 10.

Next, you need to compute the average price for the first five days (i.e. for values in index 0-4 of your array), and store it in ffAvg, you can do this using the following simple for loop:

double sum;
for( int i = 0; i < 5; i++ )
{
       sum += gasPrice[i];
}
double ffAvg = sum / 5;

You then do this with the 2nd 5 days, storing the average in lfAvg.

The next part of your task is to compare the averages, you can doing this using if and else if statements, for example, if you wanted to compare to numbers, num1 and num2 you might do the following:

if( num1 > num2 )
{ /* Do something */ }

This will compare num1 and num2 and if num1 is greater than num2 it will perform the code in the braces.

To do the last comparison you simply combine what we have done above on a per day basis. Try to experiment with various ways of doing it, as this will help you to learn more.

Hope this helps you! :)

EDIT: I also noticed that you've not closed a lot of your bracers, you must always do this so the compiler can work properly. Every { must have a corresponding }, else the compiler should throw up errors, and not compile.

André Puel · Accepted Answer · 2011-07-24 21:39:48Z

0

I sugest doing as following:

double average1=0.0;
for(int i=0;i<5;++i) {
   average1 += values[i];
}
average1/=5.0;

double average2=0.0;
for(int i=5;i<10;++i) {
   average2 += values[i];
}
average2/=5.0;

Also, take a look at std::vector, it may help you in further exercises: http://www.cplusplus.com/reference/stl/vector/

answered Jul 24, 2011 at 21:39

André Puel

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Comments

cellcortex · Accepted Answer · 2011-07-24 21:40:45Z

0

You should first compute the average of the first and last 5 days. The average is defined by the sum divided by the number of items. So your average will be (gasPrice[0] + gasPrice[1] + gasPrice[2] + gasPrice[3] + gasPrice[4]) / 5.0.

You should probably make this computation in a loop similar to the one you have for getting the input. The loop should only iterate 5 times.

answered Jul 24, 2011 at 21:40

cellcortex

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