How to make sure the transaction fails

Question

I have written a program, where if the value of dog is greater than 0 I want my cat to fail.

use anchor_lang::prelude::*;

// This is your program's public key and it will update
// automatically when you build the project.
declare_id!("3QGcf8dpdhDpTrF1Q7i9QDZH1FtB6KKrYT5ZZJF5C4ZK");

#[program]
mod hello_anchor {
    use super::*;
    pub fn initialize(ctx: Context<Initialize>) -> Result<()> { 
        //msg!("The value after initializing is {} {} {} ", value.dog,value.cat,value.color);// Message will show up in the tx logs
        Ok(())
    }
    pub fn dog(ctx:Context<Value1>,data:u8) -> Result<()> {
        let dognumber =&mut ctx.accounts.dog;
        dognumber.dog = data;
        msg!("value of dog number is {}",dognumber.dog);
        Ok(())
    }
    pub fn cat(ctx:Context<Value2>,data:u8,color:String) -> Result<()> {
        if ctx.accounts.cat.dog == 0{
            let catnumberandcolor  =&mut ctx.accounts.cat;
            catnumberandcolor.cat = data;
            catnumberandcolor.color = color;
            Ok(())
        }
        else{
            break;
        }
    }

    
}

#[derive(Accounts)]
pub struct Initialize<'info> {
    // We must specify the space in order to initialize an account.
    // First 8 bytes are default account discriminator,
    // next 8 bytes come from NewAccount.data being type u64.
    // (u64 = 64 bits unsigned integer = 8 bytes)
    #[account(init, payer = signer, space = 8 + 32)]
    pub world: Account<'info, NewAccount>,
    #[account(mut)]
    pub signer: Signer<'info>,
    pub system_program: Program<'info, System>,
}

#[derive(Accounts)]
pub struct Value1<'info> {
    #[account(mut)]
    pub dog:Account<'info,NewAccount>,
}

#[derive(Accounts)]
pub struct Value2<'info> {
     #[account(mut)]
    pub cat:Account<'info,NewAccount>,
}
#[account]
pub struct NewAccount {
    cat:u8,
    dog:u8,
    color:String,
}

If the value of dog is greater than 0 I want it to fail. Please do let me even know how I can directly get the value of dog upon calling the function dog in the if/else statement.

Answer 1

Can use: https://docs.rs/anchor-lang/latest/anchor_lang/macro.require_gte.html

Pass it your custom error so it will be easy to understand why it failed in the transaction log.