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arrays proplem

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arrays proplem

Dec 28th, 2007

hello ,Im a new member and Im not very good in english , so please excuse me , I have question :
write a C++ program that declares an array alpha of 50 component of type double . Initialize the array so that the first 25 components are equal to the square of the index variable , and the last 25 components are equal to the three times the index variable . output the array so that 10 elements per line are printed .

what does it this mean Initialize the array so that the first 25 components are equal to the square of the index variable ?

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Re: arrays proplem

Dec 28th, 2007

>what does it this mean Initialize the array so that the first 25
>components are equal to the square of the index variable ?
I would assume something like this:

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 C++ Syntax (Toggle Plain Text) 
for ( int i = 0; i < 25; i++ )
  alpha[i] = i * i;
for ( int i = 0; i < 25; i++ )
  alpha[i] = i * i;

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Re: arrays proplem

Dec 28th, 2007

Once you declare an array you just reserve some amount of memory. This memory contains garbage. if you try to print all values of the array just after delaring it you will see just garbage. See folowing line of code.

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 C++ Syntax (Toggle Plain Text) 
int alpha[50];
int i = 0;
for(i=0;<50;++i)
{
    cout<<alpha[i]<<"  ";
}
int alpha[50];
int i = 0;
for(i=0;<50;++i)
{
    cout<<alpha[i]<<"  ";
}

Initialization means providing valid values to elements for the first time.
Narue's code intializes first 25 elements of the array. You can try initializing rest.

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Lerner

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Re: arrays proplem

Dec 28th, 2007

I thought this was initialization:

int num[] = {1, 2, 3, 4};

and this:

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int num[4];
for(int i = 0; i < 4; i++i)
  num[i] = i;
int num[4];
for(int i = 0; i < 4; i++i)
  num[i] = i;

represented serial assignment.

Furthermore I think that either the instructor, the OP, or I (and I don't think it's me this time) don't know the difference between iniatialization of the elements of an array and assignment to the elements of an array and use the two concepts interchangeably, as they can end up with the same result.

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Re: arrays proplem

Dec 28th, 2007

I believe we are confused in Initialization and declaration.

int i ; // declaration
int i = 10 ; declaration + initialization

i= 15 ; // assignment

You cannot only do initialization without declaration.

As per the initial question is concerned it is stupid to initialize the array with different values.

int alpha [50] = {1,2*2,3*3,…………………} ;// wrong syntax

int alpha[50] = {0} ; //initialize all the fifty elements by 0

Naure’s solution presumes taht the instructor wants to *assign* values to the array not exactly initialize. I agree with the solution.

Last edited by dubeyprateek; Dec 28th, 2007 at 7:22 pm.

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Re: arrays proplem

Dec 29th, 2007

before every thing thank you for helping , and Im asking if these answer is right :

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
# include <iostream>
using namespace std ;
int main ()
{
int alpha[50];
for (int i=0;i<25;i++)
{
alpha[i]=i*i;
cout<<alpha[i]<<" ";
for(i=25;i<50;i++)
{
alpha[i]=3*i;
cout<<alpha[i]<<" ";
}
return 0
}
# include <iostream>
using namespace std ;
int main ()
{
int alpha[50];
for (int i=0;i<25;i++)
{
alpha[i]=i*i;
cout<<alpha[i]<<" ";
for(i=25;i<50;i++)
{
alpha[i]=3*i;
cout<<alpha[i]<<" ";
}
return 0
}

also I have question how can I print 10 elements per line if I had 2 loop
and thank you very much ,

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Re: arrays proplem

Dec 29th, 2007

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Originally Posted by bis student

before every thing thank you for helping , and Im asking if these answer is right :
Help with Code Tags

C++ Syntax (Toggle Plain Text)
# include <iostream>
using namespace std ;
int main ()
{
int alpha[50];
for (int i=0;i<25;i++)
{
alpha[i]=i*i;
cout<<alpha[i]<<" ";
for(i=25;i<50;i++)
{
alpha[i]=3*i;
cout<<alpha[i]<<" ";
}
return 0
}
# include <iostream> using namespace std ; int main () { int alpha[50]; for (int i=0;i<25;i++) { alpha[i]=i*i; cout<<alpha[i]<<" "; for(i=25;i<50;i++) { alpha[i]=3*i; cout<<alpha[i]<<" "; } return 0 }
also I have question how can I print 10 elements per line if I had 2 loop
and thank you very much ,

You're on the right track. Another solution would be to use only one for loop and use an if else test condition to test for the first 25, do whatever...

As regards printing 10 per line, you could make use of the % modulus operator to determine whether a newline should be printed if (i % 10 == 0) .

I hope this is of value.

Steve
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invisal

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Re: arrays proplem

Dec 29th, 2007

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Originally Posted by superjacent

You're on the right track. Another solution would be to use only one for loop and use an if else test condition to test for the first 25, do whatever...

If you want to use only one loop, you don't need to use condition.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
for(int i =0; i<25; i++) {
   alpha[i] = i * i;
   alpha[49-i] = (49-i) * 3;
}
for(int i =0; i<25; i++) {
   alpha[i] = i * i;
   alpha[49-i] = (49-i) * 3;
}

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Re: arrays proplem

Dec 30th, 2007

thank you again for helping , and I want another hint about print 10 elements per line because this if (i % 10 == 0) does is not work .

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Re: arrays proplem

#10

Dec 30th, 2007

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Originally Posted by bis student

thank you again for helping , and I want another hint about print 10 elements per line because this if (i % 10 == 0) does is not work .

After you successfully initialize your array, you create another loop for print each element of your array. Every 10 elements, you insert the newline character. (Hint: everytimes the counter is divisable by 10, then it means you have already print 10 elements in that line)

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