CODEWITHSUNDEEP
c++
user2852575
user2852575

Reputation:

C++ array issue

I am new with C++, so I need your help. I wrote this program, 

#include<iostream.h> 

int main(){
     int totalAge = 0;
     int age[10];

     for(int j= 1; j<10; j++){
              age[j] = j;
             cout << age[j] << endl;
     }

     for(int i = 0; i<10; i++){
             totalAge = age[i];
           cout << "Total Age is : " << totalAge << endl;           
     }
     system("pause");
}

Where as the output on command prompt is this:

1 2 3 4 5 6 7 8 9

Total Age is : 1700868285

Total Age is : 1

Total Age is : 2

Total Age is : 3

Total Age is : 4

Total Age is : 5

Total Age is : 6

Total Age is : 7

Total Age is : 8

Total Age is : 9

Press any key to continue . . .

The only thing I want to know is that why is first "Total Age is : 1700868285" I believe it should be "Total Age is : 0" Please explain it. Thanks

Upvotes: 2

Views: 131

Answers (6)

Ade Miller
Ade Miller

Reputation: 13743

Your first loop never initialized age[0]. In some languages variables are automatically set to their default value. C++ is not one of them. C++ makes no guarantees about the value of an uninitialized variable. The 1700868285 value is simply whatever happened to be in the memory used to store age[0] when interpreted as an int.

Your code should read like this. Now age[0] is set to 0.

for(int j = 0; j < 10; j++)
{
    age[j] = j;
    cout << age[j] << endl;
}

This is a good example of why you should be very diligent about initializing variables in C++. As pointed out below by @Caesar you could start off by declaring the array and initializing it at the same time. This adds a small overhead in that you have written zeros into the array and then update it with the values you really want but this will help avoid the issue that caught you here.

You can actually do this using std::array (as pointed out by @Ben) and std::iota from the Standard Library which will make your code simpler.

std::array<int, 10> age = { 0 };      // initialize all the values to zero.
std::iota(begin(age), end(age), 0);   // Set the values of the elements to 0...9

If you want to make even more C++ like you can also consider using the new form of for syntax.

for (auto a : age)
{
    totalAge = a;
    cout << "Total Age is : " << totalAge << endl;
}

And consider using the std:accumulate algorithm, rather than manually calculating the sum.

int totalAge = std::accumulate(begin(age), end(age), 0);

Upvotes: 5

CharlieScarver
CharlieScarver

Reputation: 21

Your first loop starts from 

int j= 1;

and the first element of the array is age[0]. In the second loop you're trying to get the value of age[0] and since it was never initialized you receive this long ass address number.

Upvotes: 0

user3124010
user3124010

Reputation:

In your first for loop, you assign array index 1 to 1. Array index 0 is the first, which is left unassigned to anything, which means that it can have any value (because it's uninitilized). Then, in your second for loop, you access that index, which has an uninitilized value.

I think you want to change your first for loop to look something like this:

 for(int j = 0; j < 10; j++){
     age[j] = j;
     cout << age[j] << endl;
 }

Note that the only change is that it now starts from 0.

Upvotes: 0

Gaurav Sehgal
Gaurav Sehgal

Reputation: 7542

Array indexing begins from zero.While inputting you have given no value to age[0] while at the time of outputting you are using age[0] which gives a garbage value.So run your first loop from 0 to 9.

Upvotes: 0

Caesar
Caesar

Reputation: 9853

The reason you have this issue is because you never set the value for the first element in the array age. Therefore, it is value is undefined.

An easy fix is to declare your array like this int age[10] = { 0 };, initializing all the values in the array to zero.

Upvotes: 3

Benesh
Benesh

Reputation: 3428

You never initialize age[0], becuase j is never equal to 0. So in the second loop, when i=0, totalAge is assigned the uninitialized value age[0] which contains garbage value.

Upvotes: 1

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