Calling Other Contract

EVM

contract A {
  address private _hello = 0x6e110......011e6;
  
  function hello() external {
    IHello(_hello).hello(10);
  }
}

interface IHello {
  function hello(uint256 times) external;
}

contract Hello {
  mapping(address caller => uint256 times) public contacted;
  
  function hello(uint256 times) external {
    contacted[msg.sender] += times;  
  }
}

Solana

In Solana it is called cross-program invocation (CPI). To make a CPI you need to provide the program address, accounts and arguments.

#[account]
pub struct Caller {
  pub caller: Pubkey,
  pub times: u64,
}

let cpi_accounts = cpi::accounts::Hello {
    caller: ctx.accounts.caller.to_account_info(),
};

let cpi_context = CpiContext::new(
    ctx.accounts.hello_program.to_account_info(),
    cpi_accounts,
);

let times = 10;
cpi::hello(cpi_context, times)?;

A signature is sometimes required (e.g. the destination program pulls funds from source program accounts) and you can use new_with_signer to create the context

let cpi_accounts = cpi::accounts::Hello {
    authority: ctx.accounts.caller.to_account_info(),
};

let authority_seeds = &[
    b"authority".as_ref(),
    &[ctx.bumps.authority],
];
let authority_signer = &[&authority_seeds[..]];

let cpi_context = CpiContext::new_with_signer(
    ctx.accounts.hello_program.to_account_info(),
    cpi_accounts,
    authority_signer,
);

let times = 10;
cpi::hello(cpi_context, times)?;

Without using cpi

#[derive(AnchorSerialize, AnchorDeserialize)]
pub struct InstructionArguments {
    arg1: u64,
    arg2: u64,
}

let accounts = vec![
  AccountMeta::new(ctx.accounts.payer.key(), true), // signer, mutable
  AccountMeta::new(ctx.accounts.mutable_non_signer.key(), false),
  AccountMeta::new_readonly(ctx.accounts.immutable_non_signer.key(), false)
];

// Get discriminator from the Function Selector page
let mut data = vec![1, 2, 3, 4, 5, 6, 7, 8];

let ix_data = InsturctionArguments {
  arg1: 1,
  arg2: 2
};

ix_data.serialize(&mut data)?;

let instruction = Instruction {
    program_id: ctx.accounts.program.key(),
    accounts,
    data,
};

let signer_seeds = &[
    b"signer".as_ref(),
    &[ctx.bumps.signer],
];

invoke_signed(
    &instruction,
    &[
        ctx.accounts.payer.to_account_info(),
        ctx.accounts.mutable_non_signer.to_account_info(),
        ctx.accounts.immutable_non_signer.to_account_info(),
    ],
    &[signer_seeds],
)?;