25.1.4. Three Address, Two Address, One Address, and Zero Address Instruction Formats

Now, basically what are the instruction types? So, basically even if you have look at the C program what do you have? You declare some variables, then you do some addition, multiplication, subtraction and you have loops. So, basically and some standard printf and scanf statement. So, basically no code can have anything other than this that is data transfer instructions, arithmetic and logical instructions and basically control instructions.

In programming, especially in languages like C, instructions can be generally categorized into three types: data transfer, arithmetic & logical, and control instructions. Data transfer instructions handle moving data around, arithmetic & logical instructions perform mathematical operations or logic operations, and control instructions manage the flow of the program, such as through loops or conditionals.

Think of a restaurant kitchen. The data transfer instructions are like waitstaff moving ingredients (data) from the pantry to the chef (registers). Arithmetic and logical instructions are the chefs preparing dishes (mathematical operations). Finally, control instructions are the head chef giving orders on what dish to prepare next based on customer orders (control flow).

So, whenever you say scanf, storing some variables basically they are nothing but data transfer operation; you get the value of the data from the memory, then arithmetic and logical instruction; that is the most important one like you do add subtract multiply etcetera and control like you have loops.

Data transfer operations involve getting input (like using scanf) and placing it in variables. The arithmetic and logical instructions are the core computations (like adding, subtracting), while control instructions dictate how the program flows, allowing for actions based on conditions (like loops). This categorization helps in structuring program operations.

Imagine a school classroom. The teacher (data transfer) takes attendance, the students (arithmetic/logical operations) complete math problems, and the class schedule (control) determines what subject to study next. Each part needs to function correctly to keep the day running smoothly.

Now, again as I told you three address instruction format is that there will be opcode destination source and source. This is a special type of an instruction means similar addition compared to this add instruction.

The three address instruction format allows specifying three operands: an opcode (the operation to perform), a destination (where the result goes), and two sources (the values to operate on). This versatility can lead to complex operations in fewer instructions, though it can increase the instruction complexity.

Think of ordering coffee with ingredients. You might say, 'Add sugar (source1) and cream (source2) to my coffee (destination).' This way, you specify exactly how you want your drink prepared in one instruction instead of having to order sugar and cream separately.

2 instruction format is the most widely accepted. It says that opcode source source; that means, what happen is that sometimes actually like as I showed you ADD R1, R2 that means it says that; whatever is the value of R1 value of R2 you have to add to R1 and store back.

In the two address instruction format, the result is stored back in one of the sources. This means one operand is both a source value and destination for the result, leading to simpler instructions. The compactness of these instructions typically makes them easier to execute by the CPU.

Consider a chef making a sandwich. If the chef takes the bread (source1) and adds ham (source2), the sandwich is now reassembled with new ingredients (the result is stored in bread). Thus, the same piece of bread serves as both the source and destination.

In this case as I told you one is a de facto standard is the accumulator; that means, whenever I say add 3030, if nothing is mentioned, that is a register which is the accumulator.

One address instruction formats rely on an accumulator, a designated register where the result of operations is stored. For instance, an operation might only need one operand explicitly stated since the accumulator is implied. This reduces instruction length but increases the number of instructions needed to complete tasks.

Think of a simple notepad. If you can only write one thing down at a time (using an accumulator), you might need to write multiple times to achieve the same effect as writing everything at once. However, it simplifies the writing because there's only one space to manage.