loop though a array then if and then output result?

i have a little problem, in the code below (C#) it loops thought the arrays, it then check if the user_id has a user_post greater than 50, it then writ开发者_如何转开发e the user_id, the expected outcome is

12
13

but the actual output is

12
12
12

whats wrong with the code? I tried a standard for loop but could not get it right?

int[] user_id = new int[64];
int[] group_id = new int[64];
int[] user_post = new int[64];

//user 55
user_id[0] = 10;
group_id[0] = 8;
user_post[0] = 4;

//user56
user_id[1] = 11;
group_id[1] = 2;
user_post[1] = 15;

//user57
user_id[2] = 12;
group_id[2] = 2;
user_post[2] = 55;

//user58
user_id[3] = 13;
group_id[3] = 2;
user_post[3] = 56;

foreach (int i in group_id)
{
    if (group_id[i] == 2)
        if (user_post[i] > 50)
            Console.WriteLine(Convert.ToString(user_id[i]));
}

Console.WriteLine("Press any key too continue...");
Console.ReadLine();
// continue...

Because you have an if statement that only checks for 2

 if (group_id[i] == 2)

where as "i" is not a counter instead the element from the foreach loop. and items at 2 & 3rd position have 2 group id so it alway ends like this:

if (group_id[8] == 2) //false
if (group_id[2] == 2) //true
if (group_id[2] == 2) //true

Instead of that vague code you should have your loop as this:

for(int i = 0 ; i< 64 ; i++)
{
    if (group_id[i] == 2)
    {
        if (user_post[i] > 50)
        Console.WriteLine(Convert.ToString(user_id[i]));
    }

}

in your foreach statement, i takes on the values stored in your group_id array - 8, 2, 2, 2

In your if and output statements, your are using this value as an index into the arrays

So, your if statements end up doing this:

if(group_id[8])...
if(group_id[2])...
if(group_id[2])...
if(group_id[2])...

You are only examining elements 8 and 2 in your arrays.

Use a for loop to iterate through the array indexes

The for syntax is as follows:

for (int i = 0; // incremental variable
     i < 100;   // determining a limit
     ++i)       // increment the variable

While foreach works like this:

foreach (var element        // the element itself, not an index
         in
         elementCollection) // iterating through the collection

You're looping around the wrong array with the for each statement. You should loop using the regular for statement instead like this:

    for (int i = 0;i < user_post.Length; i++)
    {
        if (user_post[i] > 50 && group_id[i] == 2)
        {
          Console.WriteLine(Convert.ToString(user_id[i]));
        }
    }

foreach (int i in group_id)

is wrong, you must use:

for(int i = 0; i < group_id.Length; i++)

because with the former you're using the values in group_id as indexes of your arrays.

BTW, I'd suggest you to create a class e.g. Info like:

class Info
{
   public int GroupId {get; set;};
   public int UserId {get; set;};
   public int PostId {get; set;}
}

this would allow you to create one array only (i.e. Info[]) and avoid possible errors due to different lenghts of the 3 arrays...