Array access errors

[kiemxai]

use funtion to count this sum:
s=a1*a2+a2*a3+a3*a4+...
I did,but have error:

#include "stdafx.h"
#include<iostream>
#include<cmath>
using namespace std;
void sum(int a[],int n)
{
    int sum;
    sum=0;
    for(int i=1;i<n;i++)
        sum=sum+ a[i]*a[i+1];
    cout<<"sum="<<sum<<endl;
}
int main()
{
int *a[100];
int n;
cout<<"enter n:"<<endl;
scanf("%d",&n);
cout<<"enter numbers of array ";
for(int i=1;i<n;i++)
 
scanf("%d ",&a[i]);
sum(a[100],n);
getchar();
}
 

can you send me your answer into my email : (removed)
thank you very much !

[Banfa]

    for(int i=1;i<n;i++)
        sum=sum+ a[i]*a[i+1];
 

What values does i take in the for loop?
When i = n-1 what is the second line calculating?
What is the valid range for the index i when a has n entries?

int *a[100];
int n;
...
scanf("%d",&n);
...
scanf("%d ",&a[i]);
 

What is the type of the second parameter passed to scanf the first time it is call?
What is the type of the second parameter passed to scanf the second time it is call?
Which is correct?

[whodgson]

You appear to be asking the program to predict what is in the array element
a[i+1]. It could certainly recover the value of a[i-1]. Would a[i]*a[i-1] serve the purpose?

[newb16]

int *a[100];
This is an array of 100 pointers to integer, pointing to nowhere. You use them to store some numbers, it's wrong.

[donbock]

@kiemxai
The '...' leaves the last term of the summation to the imagination.

Which is correct for an array of five elements:
s = a1*a2 + a2*a3 + a3*a4 + a4*a5
or
s = a1*a2 + a2*a3 + a3*a4 + a4*a5 + a5*1

[kiemxai]

if I do not use the cursor when declared array:

int *a[100];

have the following error:
error C2664: 'sum' : cannot convert parameter 1 from 'int' to 'int []'
so I use the cursor is wrong.can you help me edit that code

[Savage]

Here:

sum(a[100],n);

,you are passing a single element of array to the function which expects an array of elements.Pass the whole array instead (sum(a,n);) and it's going to do fine when you remove the 'cursor'.And watch out how arrays are indexed in c/c++.

This might help http://bytes.com/topic/c/insights/77...rrays-revealed

[kiemxai]

@Savage

I do not know much about the cursor. you can for example on my code?
thanks

[kiemxai]

I used function and declare the array as follows,but still fails:

#include "stdafx.h"
#include<iostream>
#include<cmath>
using namespace std;
void sum(int (*a)[100],unsigned int n)
{
int sum;
sum=0;
for(int i=1;i<n;i++)
sum=sum+ a[i]*a[i+1];
cout<<"sum="<<sum<<endl;
}
int main()
{
int a[100];
int n;
cout<<"enter n:"<<endl;
scanf("%d",&n);
cout<<"enter numbers of array ";
for(int i=1;i<n;i++)

scanf("%d ",&a[i]);
sum(a[100],n);
getchar();
}