While high-level programming languages like C++ make arithmetic operations incredibly simple, delving into inline assembly offers valuable insights into how the CPU processes instructions under the hood. Hence in this post, we’ll walk through a simple program that uses both C++ and inline assembly to add two integer values. Additionally, we will carry out decimal adjust after addition.

Code

#include<iostream.h>
#include<conio.h>
#include<stdio.h>
void main()
{
clrscr();
int a,b,c;
cout<<"Enter First Number:";
cin>>a;
cout<<"Enter Second Number:";
cin>>b;
    asm mov ax, a     // Move first number into AX
    asm mov bx, b     // Move second number into BX
    asm add ax, bx    // Add BX to AX
    asm daa           // Decimal Adjust AL after Addition 
    asm mov c, ax     // Move result into variable 'c'
cout<<"Result:";
cout<<c;
getch();
}

Understanding the Code

Variable Declarations

• int a, b, c; → Declares three integer variables to store the two input values and their sum.

User Input

• The program prompts the user to enter two integer values, which are then stored in variables a and b.

Inline Assembly Operations

• asm mov ax, a → Moves the first number into register AX.
• asm mov bx, b → Moves the second number into register BX.
• asm add ax, bx → Adds the contents of BX to AX; the result is stored in AX.
• asm daa → Decimal Adjust AL after Addition (used for BCD arithmetic).
• asm mov c, ax → Moves the result from AX into variable c.

Output Display

• The final sum stored in c is displayed to the user using cout.

What is DAA (Decimal Adjust after Addition)?

The DAA instruction stands for Decimal Adjust after Addition. It’s an x86 assembly instruction that’s specifically designed to work with Binary-Coded Decimal (BCD) values — a format where each nibble (4 bits) represents a single decimal digit (0–9).

DAA is used after adding two BCD numbers to correct the result so it forms a valid BCD number.

For example, let’s say:

• You add 9 (1001 in BCD) and 5 (0101 in BCD).
• The raw binary result is 14 (1110 in binary), but that’s not a valid BCD digit.
• DAA corrects it to 0001 0100, which is 1 and 4 — representing decimal 14 in BCD.

Output

Enter First Number: 500
Enter Second Number: 617
Result: 1123

As shown, the inline assembly successfully computes the sum of the two integers and stores the result.