For loop code not working right?
显示 更早的评论
Question: Set the variable p9 to equal 7. Then run a for loop which goes through the numbers n = 0, 3, 6, 9, ..., 300 and adds them each in turn to p9 (changing it each time).
Code:
p9=7;
for p9=[0:3:300];
disp(num2str(p9));
p9=p9+n;
end;
This is giving me the wrong answer and I am not sure why? Thanks for your help!
1 个评论
Stephen23
2015-2-9
disp works just fine on numeric data, you don't need the num2str.
回答（2 个）
James Tursa
2015-2-9
1 个投票
You have used the variable p9 as your loop index AND as the accumulation variable. Use a different variable name for the loop index, e.g. use k=0:3:300 instead of p9=0:3:300. Then you can add k to p9 in your loop (instead of n ... where does n come from?).
8 个评论
Bob
2015-2-9
编辑：James Tursa
2015-2-9
Your variable n is defined to go from 0 to 300 in steps of three. You have variable p9 defined as being the cumulative sum of itself starting from p9=7, plus the loop iterator variable n in each step. This is clearly going to be a much bigger value than 300. And that is what you are displaying in your loop.
Try displaying the n variable, and you will see that it goes up to 300, just like it should:
p9 = 7;
for n = 0:3:300
disp(n)
p9 = n + p9,
end
Bob
2015-2-9
The loop variable does stop at 300, just like was asked.
"Then run a for loop which goes through the numbers n = 0, 3, 6, 9, ..., 300 and adds them each in turn to p9" states quite clearly that the loop variable n should go from 0 to 300. How would you interpret that? What should stop at 300? p9 or the loop variable n?
Bob
2015-2-9
James Tursa
2015-2-9
编辑：James Tursa
2015-2-9
No. The loop index "k" (or Stephen uses "n") stops at 300. The accumulated sum variable "p9" will end up being 7 + 0 + 3 + ... + 300.
Bob
2015-2-9
James Tursa
2015-2-9
If you understand the code, then I think you are done also.
Image Analyst
2015-2-9
0 个投票
In a for loop, if you change the loop iterator variable, your "p9", inside the loop, it will have that value for the remainder of that iteration of the loop. However, once it hits the end and start the next iteration of the loop, it will have the value that it would have had, had you not changed it - it will not have anything to do with what value you changed it to.
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
2015-2-9
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
