arrays proplem
 

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 ?

Re: arrays proplem
 

>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:

for ( int i = 0; i < 25; i++ )

  alpha[i] = i * i;

Re: arrays proplem
 

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.

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.

Re: arrays proplem
 

I thought this was initialization:

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

and this:

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.

Re: arrays proplem
 

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.

Re: arrays proplem
 

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

# 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 ,

Re: arrays proplem
 

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.

Re: arrays proplem
 

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

for(int i =0; i<25; i++) {

   alpha[i] = i * i;

   alpha[49-i] = (49-i) * 3;

}

Re: arrays proplem
 

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 .

Re: arrays proplem
 

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)