Array Program Weird Output

Question

I am trying to write a code to list gas mileage, and so far it works. The problem is that it does not work the way it should. The code below asks for input and then displays a list of said input along with the calculated MPG.

#include<iostream>
using namespace std;
//function prototype
void CalcAverage (int arr1[], float arr2[], int size);
//global variables
int mil [3];
float gal [3];
float mpg [3];
//main program
int main()
{
char month [7];
int day [3];
cout << "Please enter the starting month" << endl;
cin >> month;

cout << "Please enter starting day entry 1" << endl;
cin >> day [0];
cout << "entry 2" << endl;
cin >> day [1];
cout << "entry 3" << endl;
cin >> day [2];
cout << "entry 4" << endl;
cin >> day [3];

cout << "Please enter gallons entry 1" << endl;
cin >> gal [0];
cout << "entry 2" << endl;
cin >> gal [1];
cout << "entry 3" << endl;
cin >> gal [2];
cout << "entry 4" << endl;
cin >> gal [3];

cout << "Please enter miles entry 1" << endl;
cin >> mil [0];
cout << "entry 2" << endl;
cin >> mil [1];
cout << "entry 3" << endl;
cin >> mil [2];
cout << "entry 4" << endl;
cin >> mil [3];

CalcAverage (mil,gal,4);

cout << "Week of" << "\t\tGallons" << "\t\tMiles" << "\t\tMPG" << endl;
cout << "_ _ _ _ _ _ _" << "\t_ _ _ _ _" << "\t_ _ _ _"  << "_ _ _ _" << endl;
cout << month <<  " " << day [0] << "\t" << gal [0] << "\t\t" << mil [0] << "\t\t" << mpg [0] <<     endl;
cout << month <<  " " << day [1] << "\t" << gal [1] << "\t\t" << mil [1] << "\t\t" << mpg [1] <<     endl;
cout << month <<  " " << day [2] << "\t" << gal [2] << "\t\t" << mil [2] << "\t\t" << mpg [2] <<     endl;
cout << month <<  " " << day [3] << "\t" << gal [3] << "\t\t" << mil [3] << "\t\t" << mpg [3] <<     endl;

system("PAUSE");

}
//function definition
void CalcAverage (int arr1[], float arr2[], int size)
{
//statements
mpg [0] = mil [0] / gal [0];
mpg [1] = mil [1] / gal [1];
mpg [2] = mil [2] / gal [2];
mpg [3] = mil [3] / gal [3];

}

The code works and I do not get any errors. However, when the code displays the output, some of the results are switched or jumbled, or completely random (my 3rd gal input becomes my 1st mil input etc.) What is causing this problem, and how can I fix it?

rcs · Accepted Answer · 2013-10-24 02:43:46Z

2

Note that when you declare an array like mil[3], the array has elements of mil[0], mil[1], and mil[2]. Thus it is not valid to use mil[3]. Change your array declaration to:

int mil [4];
float gal [4];
float mpg [4];

Also the day to use [4] instead of [3]

answered Oct 24, 2013 at 2:43

rcs

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Comments

John Kugelman · Accepted Answer · 2013-10-24 02:43:15Z

2

The arrays are all size 3 and you're trying to stuff 4 values into each. Increase their sizes by one:

int mil [4];
float gal [4];
float mpg [4];

...

int day [4];

answered Oct 24, 2013 at 2:43

John Kugelman

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Comments

Crowman · Accepted Answer · 2013-10-24 02:42:40Z

1

You do things like:

cin >> day [3];

but you only have:

int day [3];

You're overwriting the end of your array and into the next one. You need to change that to int day[4], since day[3] is the fourth element, not the third.

answered Oct 24, 2013 at 2:42

Crowman

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Comments

elune · Accepted Answer · 2013-10-24 02:44:27Z

1

change with this :

int mil [4];
float gal [4];
float mpg [4];

int day [4];

answered Oct 24, 2013 at 2:44

elune

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