Adding and subtracting from a base value.

I mean I want use 5 as a base value and using += makes it 6 and when I use -=2 from it it becomes 4.

But the situation is different when I use += it 1becomes 6，but after I use -=1 it becomes 4 not 5.
This is very annoying minor issue :/.

 

There's probably a simple logical error in your code.

 

They are in two different methods/functions.

 

If the variable exists in each method as a local variable, they won't affect each other. If not, post a script that we can have a look at.

 

Public int counter;
{
Public void btnr ()
{
If (counter > 9)
{
counter = 0;
}
spriteindex = [counter];
counter += 1;
}

Public void btnl ()
If (counter = 1)
{
counter = 0;
}
spriteindex = [counter];
counter -= 1;
}

This was typed from my mobile so it may have errors.

 

There are some errors such as a missing '}' (second method) and the condition counter = 1 in the second method will always be true. Not sure whether it's a typo as you said you're posting from the mobile phone, but it has to be '=='.
Also, the second method does not make alot of sense to me, what are you trying to achieve with those?

 

If you press the right button it changes to the next sprite in the array and if you press the left button it changes to a previous sprite.

And when the counter reaches maximum/minimum value interests itself.

9 max and 1 min

 

There are several issues with the code you provided. Assuming is because you typed it in via a phone, I won't worry about the index stuff. Basically cleaned up it should look something like this:

Code (CSharp):

1.     public int counter;
2.     public void btnr ()
3.     {
4.         counter += 1;
5.         if (counter > 9)
6.         {
7.             counter = 0;
8.         }
9.     }
10.  
11.     public void btnl ()
12.     {
13.         counter -= 1;
14.         if (counter < 0)
15.         {
16.             counter = 9;
17.         }
18.     }

This assumes you are stepping through an array, so the values would be 0-9. You inc/dec the counter then wrap it.
Though for something like this I usually use a ternary or "?" operator.

Code (CSharp):

1.  
2.     public int counter;
3.     public int counter_max = 9;
4.  
5.     public void btnr ()
6.     {
7.         counter = (counter+1 > counter_max) ? 0 : counter+1;
8.     }
9.  
10.     public void btnl ()
11.     {
12.         counter = (counter-1 < 0) ? counter_max : counter-1;
13.     }

 

your code is okay but it still doesn't produce the results I want.

when I press left button it changes sprite 3 to sprite 2, but after I press the right button it changes from sprite 3 to 4 instead. This is my issue.

 

Post the updated code with code tags (copy/paste, please not type it from mobile again).
The code provided by @zombiegorilla looks correct to me.

 

It sounds like you are not changing the base value then. As @Suddoha suggested, please paste your complete code.

 

using UnityEngine;
using System.Collections;

public class imagechanger : MonoBehaviour {

// Use this for initialization
public Sprite[] sprites;
public GameObject mouth;
public SpriteRenderer spriteRenderer;
public int counter;
public void clickpos()
{
switch(counter)
{ case 0:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 1:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 2:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 3:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 4:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 5:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 6:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 7:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 8:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 9:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 10:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 11:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 12:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 13:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 14:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 15:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 16:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 17:
counter += 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
case 18:
counter = 0;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
break;
}
}

public void clickneg()
{
counter -= 1;
spriteRenderer.sprite = sprites[counter];
Debug.Log(counter);
}
}

Code which I wrote.

 

First, please use code tags.

Not sure why you are using a switch, this will do the trick:

Code (CSharp):

1.     public SpriteRenderer spriteRenderer;
2.     public Sprite[] sprites;
3.     public int counter;
4.  
5.     public void clickpos()
6.     {
7.         counter = (counter+1 < sprites.Length) ? counter+1 : 0;
8.         spriteRenderer.sprite = sprites[counter];
9.         Debug.Log(counter);
10.     }
11.  
12.  
13.     public void clickneg()
14.     {
15.         counter = (counter-1 >= 0) ? counter-1 : sprites.Length-1;
16.         spriteRenderer.sprite = sprites[counter];
17.         Debug.Log(counter);
18.     }

Edit: Array of sprites not strings.

 

It still doesn't show the result I want, when the value is 4 I press the positive arrow it becomes 5, but when I press the negative arrow it becomes 1, I want it to be 4 instead.

 

That code snippet works as expected. Something else is going on that is affecting it. Are you setting the counter elsewhere? Are key strokes counting more than once? Are you only using the code in one place? are you changing the array elsewhere?

Please post your complete script as you have it in the game. (in code tags). I am guessing something else it affecting the counter value.

 

I got it I think so， I'm using the same script on two different objects，instead I should call the method from a single script using getComponent I suppose.

I'll try it and post updates.

 

Heh... that would definitely cause the problem you are seeing. Sadly, I have done that same thing on more than one occasion, trying to debug a script, when the problem was it was attached in the wrong place or duplicated.