c-02-function-sum-descending-numbers-of-n-to-1.asm

// This program takes user input and calculates the sum of descending
// numbers from the input down to 1, and then outputs the result.
//
// int sum = 0;
// const int one = 1;
// int input;
// cin >> input; 
// do {
//     sum += number;
//     number = number - one;
// } while (number > 0);
// cout << sum;

lbResetVars     STA varSum         // Accumulator has 0, and Sum is reset to 0
                INP                // Take user input and store it in Accumulator

lbAddNumber     STA varNumber      // Store the input value in memory location varNumber
                ADD varSum         // Add the sum to the input value 
                STA varSum         // Store the updated sum back in varSum

lbDecrement     LDA varNumber      // Load the input value back into the Accumulator
                SUB valOne         // Subtract 1 from the input value
                BRP lbAddNumber    // If the result is positive, branch back to lbAddNumber

lbOutput        LDA varSum         // Load the final sum into the Accumulator
                OUT                // Output the result
                HLT                // Halt the program

varNumber       DAT 0              // Memory location to store the input value
varSum          DAT 0              // Memory location to store the sum
valOne          DAT 1              // Constant value 1