naturalsum.c

#include <stdio.h>

int main()
{
	int sum = 0, i, n;  //set variables

	printf("Enter number integers to be sum\n");
	scanf("%d", &n); // scan for "n"
	for (i = 1; i <= n; i++)  //increment "i" until it equals "n"
	{
		sum += i;  // add up the sum
	};
	printf("Sum:%d\n", sum);  //print sum
	return 0;
};

LEGv8 code for adding up the natural numbers to user defined n

n->X19
sum->X20
i->X21

ADDI X19, X19, #0  //set n to 0 in X19
ADDI X20, X20, #0  //set sum to 0 in X20
ADDI X21, X21, #0  //set i to 0 in X21

				   //here is where you scan in "n"

	Loop:
ADD  X20, X20, X21  //sum = sum + i
SUBS X9, X19, X21   //compare n and i
B.EQ Exit         //if i = n exit
ADDI X21, X21, #1   //increment i
B    Loop         //loop

				  //print the sum
	Exit : ...

/////////////////////////////////////
ADD X20, X20, XZR //i + 1

	loop:
SUB X9, X19, X10 //
CBZ X9, Exit
ADD X20, X20, X10
ADD X10, X10, #1
B Loop

Exit : ....