+ 1

How would I solve this for loop? I am trying to get the value of the sum.

int sum =0; for(int i=0; i<5;i++) { for(int j=i-1; j>0; j--) { sum++; } }

15th Apr 2018, 2:42 AM
Cherish
Cherish - avatar
16 Respostas
+ 3
Check out the comments at the bottom of the code: https://code.sololearn.com/cSSEuIPyZTzi/?ref=app#cpp I've reproduced the comments here: Note, this is far harder than it looks to work out! So don't be disheartened as a beginner. sum = 0 i = 0 j = i - 1 = -1 for (int j = i - 1; j > 0; j--) for (int j = -1; j > 0; j--) [code doesn't run inside this for loop this time] sum = 0 i = 1 j = i - 1 = 0 for (int j = i - 1; j > 0; j--) for (int j = 0; j > 0; j--) [code doesn't run inside this for loop this time] sum = 0 i = 2 j = i - 1 = 1 for (int j = i - 1; j > 0; j--) for (int j = 1; j > 0; j--) [code runs inside this loop once] ==> sum++ sum = 1 i = 3 j = i - 1 = 2 for (int j = i - 1; j > 0; j--) for (int j = 2; j > 0; j--) [code runs inside this loop once] ==> sum++ sum = 2 for (int j = 1; j > 0; j--) [code runs inside this loop again] ==> sum++ sum = 3 i = 4 j = i - 1 = 3 for (int j = i - 1; j > 0; j--) for (int j = 3; j > 0; j--) [code runs inside this loop once] ==> sum++ sum = 4 for (int j = 2; j > 0; j--) [code runs inside this loop once] ==> sum++ sum = 5 for (int j = 1; j > 0; j--) [code runs inside this loop once] ==> sum++ sum = 6 end of for loops.
15th Apr 2018, 3:53 AM
Emma
15th Apr 2018, 3:19 AM
Emma
+ 2
You need to step through the code on paper. I'll try to explain in more detail. Give me some time.
15th Apr 2018, 3:33 AM
Emma
+ 1
It depends what you mean by 'solve'. What are you trying to do?
15th Apr 2018, 2:56 AM
Emma
+ 1
The sum of what?
15th Apr 2018, 3:02 AM
Emma
+ 1
@xan thank you so much. do you know how it got to 6? like the loop pattern and how it increments etc....? thank you again!!
15th Apr 2018, 3:22 AM
Cherish
Cherish - avatar
+ 1
okay thank you!!! I truly appreciate it! @xan
15th Apr 2018, 3:34 AM
Cherish
Cherish - avatar
+ 1
@xan thank you, I totally understand now!!!!
15th Apr 2018, 3:40 AM
Cherish
Cherish - avatar
+ 1
@Xan Wow thank you so much!!!! I really can't thank you enough!!! I truly have a full understanding now!
15th Apr 2018, 4:14 AM
Cherish
Cherish - avatar
+ 1
No problem. I was stumped at first myself, even with 30+ years programming experience! In reality, this would be considered unprofessional code if seen in the wild, but it's a good training exercise.
15th Apr 2018, 4:17 AM
Emma
0
for each iteration in the first for loop calculate all the values of the for loop inside. Btw I think i-1 in the code =-1, so the second for loop wouldn't run.
15th Apr 2018, 2:47 AM
Akib
Akib - avatar
0
because the first loop is true from the start do I increment it by 1 anyways? or what do I do?
15th Apr 2018, 2:51 AM
Cherish
Cherish - avatar
0
and the second loop is false so it would not run... but it would loop through the first 1 making i=1 then go through the second loop and it will still be false. then make the 1st one 2 and once it hits the second loop it will then be true making the sum 1 ... I think I'm still confused can you explain it more? @akib
15th Apr 2018, 3:00 AM
Cherish
Cherish - avatar
0
@xan I am trying to get the sum
15th Apr 2018, 3:01 AM
Cherish
Cherish - avatar
0
the value of sum. @xan
15th Apr 2018, 3:03 AM
Cherish
Cherish - avatar
0
e,m z,c
15th Apr 2018, 8:02 AM
DAVID SHAWN