Why the value is getting changed...?

[Manjiri]

Hello Everybody...

Here i have the program which prints how many number of times the element appears in the array....
The code is as follows...

#include<iostream.h>
 
 
class Count
{
 
int a[100],b[100],n;
 
public:
void getdata();
void cal();
void show();
 
};
 
void Count::getdata()
{
int i;
cout<<"How many numbers you want to enter"<<endl;
cin>>n;
cout<<"Enter the numbers"<<endl;
for(i=1;i<=n;i++)
cin>>a[i];
 
 
}
 
 
void Count::cal()
{
int i,j;
for(i=1;i<=100;i++)
b[i]=0;
for(i=1; i<=n; i++)
{
j=a[i];
b[j]++;
}
}
 
 
void Count::show()
{
int i;
for(i=1; i<=n; i++)
{
if(b[i]!=0)
cout<<"The number "<<i<<"is present "<<b[i]<<"times"<<endl;
}
}
int main()
{
Count c;
c.getdata();
c.cal();
c.show();
return 0;
}

Now my question is the value of n is getting changed, when i will initialise the elements of array b to 0(zero) (See the cal function)... "Why the value is getting changed..?"...

if you try to print the value of n before the for loop then it will give you the correct ans but after the for loop the value of n is getting changed, where i am not at all altering the value of n...


Plz if you have any ieda then let me know... I want the reason not output of the program i mean to say dont alter the code because as per my knowledge the code is correct.. Just tell me what is wrong with this code..

Thanks in advance
Manjiri

[horace1]

you define the arrays

int a[100],b[100],n;
 

where b has elements b[1] thru b[99] - remember C/C++ starts array indexes at 0 not 1

in cal() you have a loop

void Count::cal()
{
int i,j;
for(i=1;i<=100;i++)
b[i]=0;
 

which will assign 0 to elements b[1] to b[100] (loop terminates when i = 101) corrupting whatever follows b in memory.

change your loop to

void Count::cal()
{
int i,j;
for(i=0;i<100;i++)
b[i]=0;
 

also check your other for loops

[Manjiri]

you define the arrays

int a[100],b[100],n;
 

where b has elements b[1] thru b[99] - remember C/C++ starts array indexes at 0 not 1

in cal() you have a loop

void Count::cal()
{
int i,j;
for(i=1;i<=100;i++)
b[i]=0;
 

which will assign 0 to elements b[1] to b[100] (loop terminates when i = 101) corrupting whatever follows b in memory.

change your loop to

void Count::cal()
{
int i,j;
for(i=0;i<100;i++)
b[i]=0;
 

also check your other for loops

Hello friend

Thank you very much.... it worked but i am not yet cleared with the thing..
What happens if indexes start with 0 also... why the value n gets changed..?
Plz clear this also...

[Manjiri]

you define the arrays

int a[100],b[100],n;
 

where b has elements b[1] thru b[99] - remember C/C++ starts array indexes at 0 not 1

in cal() you have a loop

void Count::cal()
{
int i,j;
for(i=1;i<=100;i++)
b[i]=0;
 

which will assign 0 to elements b[1] to b[100] (loop terminates when i = 101) corrupting whatever follows b in memory.

change your loop to

void Count::cal()
{
int i,j;
for(i=0;i<100;i++)
b[i]=0;
 

also check your other for loops

Hey friend if i execute the same program in c(with index initialised from 1) it is getting executed then how come it is possible...?

[horace1]

Hey friend if i execute the same program in c(with index initialised from 1) it is getting executed then how come it is possible...?

what happened was that when you initialised b[] to 0 you overran the end of the array and what ever was in memory after it was zeroed - in this case it was n

int a[100],b[100],n;
 

However, the way that information is stored in memory depends upon the compiler, linker, various options, etc. , i.e. with a different compiler n may not immediatly dollow b[] in memory and the program may well appear to work OK. In such a case the error often shows up later when input data is changed or the code is ported to a different system.

[Manjiri]

what happened was that when you initialised b[] to 0 you overran the end of the array and what ever was in memory after it was zeroed - in this case it was n

int a[100],b[100],n;
 

However, the way that information is stored in memory depends upon the compiler, linker, various options, etc. , i.e. with a different compiler n may not immediatly dollow b[] in memory and the program may well appear to work OK. In such a case the error often shows up later when input data is changed or the code is ported to a different system.

Ok............... Now i got know.. Thanks friend... I appreciate your talent...

Manjiri