# 4.6. Doing Work in LoopsΒΆ

To do work in a loop, we just have to place the work we want to do in the body of the basic loop structure. Below is an example of implementing ARM assembly roughly equivalent to this C++ code:

```
int sum = 0;
int max = 10;
//r2 will be our counter "variable" - however it will just live in a register and not be stored into memory
for(r2 = 1; r2 <= max; r2++)
sum += r2;
```

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | ```
.data
sum: .word 0
max: .word 10
.text
_start:
LDR r1, =max @r1 = &max
LDR r1, [r1] @r1 = max
MOV r2, #0 @r2 is counting variable (i)
MOV r3, #0 @r3 is sum
@Use test at end loop strategy
B loopTest @Start loop by jumping to test
loopStart:
ADD r3, r3, r2 @sum += r2
ADD r2, r2, #1 @r2++
loopTest:
CMP r2, r1 @Compare counter in r2 to max in r1
BLE loopStart @branch to start if i (r2) <= y (r1)
LDR r4, =sum @r4 = &sum
STR r3, [r4] @store r3 back to sum to record final answer
``` |

You have attempted of activities on this page