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example_program_1.md

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Example program 1

Start:
INP          ; Read number from input
BRZ Output   ; If read number is a zero, go to output 
ADD Sum      ; Add the read number to the current sum value
STA Sum      ; Store the current sum value in Sum
BRA Start    ; Branch back to start to read a new number
Output:
LDA Sum      ; Load the current value of the sum
OUT          ; Copy the accumulator value to output
HLT          ; Stop the machine
Sum:
0            ; Current value of sum (start value is 0)

Program Analysis

  1. Start:

    • INP: Reads a number from the input and stores it in the accumulator.

  2. BRZ Output:

    • Checks if the number just read (now in the accumulator) is zero.
    • If it is zero, the program branches to the Output label; otherwise, it continues to the next instruction.

  3. ADD Sum:

    • Adds the value stored at the memory location labeled Sum to the accumulator. Initially, Sum is 0, so this effectively starts accumulating the sum of the input numbers.

  4. STA Sum:

    • Stores the current value of the accumulator (which now holds the sum) back into the memory location labeled Sum.

  5. BRA Start:

    • Unconditionally branches back to the Start label, causing the program to read the next input number.

  6. Output:

    • This section is reached only when a zero is input (due to the BRZ Output instruction).

  7. LDA Sum:

    • Loads the current value of Sum (the accumulated sum) into the accumulator.

  8. OUT:

    • Outputs the value in the accumulator (the total sum) to the output.

  9. HLT:

    • Halts the machine, stopping the program execution.

  10. Sum:

    • A memory location labeled Sum initialized with 0. This is used to store the running total of the input numbers.

Program Functionality

  • The program continuously reads numbers from the input and adds them to a running total.
  • When the user inputs zero, the program outputs the total sum of all previously entered numbers.
  • After outputting the sum, the program halts.

Example execution

  • If a user inputs 3, 5, 2, and then 0, the program will output 10 (since 3 + 5 + 2 = 10) and then halt.