# How do I create a for loop in MATLAB?

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pedro marin on 5 Mar 2012
Commented: Walter Roberson on 11 Jan 2023 at 18:48
I am completely lost in for loops, I just don't get it. The book and my professor haven't helped much. Where can I get help?
##### 2 CommentsShowHide 1 older comment
Walter Roberson on 14 May 2017

Walter Roberson on 5 Mar 2012
Edited: MathWorks Support Team on 9 Nov 2018
A basic for loop in MATLAB is often used to assign to or access array elements iteratively. For example, let’s say you have a vector A, and you want to simply display each value one at a time:
A = [3 6 9 4 1];
for i = 1:length(A)
disp(A(i))
end
For more examples using for loops, see:
Walter Roberson on 21 Sep 2022
Edited: Walter Roberson on 21 Sep 2022
A = randi([0 9], 1, 20)
A = 1×20
1 9 5 8 6 2 6 2 2 0 3 2 1 4 7 3 9 7 2 6
%then output in groups of 5 in vectorized form
reshape(A, 5, []).'
ans = 4×5
1 9 5 8 6 2 6 2 2 0 3 2 1 4 7 3 9 7 2 6
%or if you need a for loop
for K = 1 : 5 : numel(A); disp(A(K:K+4)); end
1 9 5 8 6 2 6 2 2 0 3 2 1 4 7 3 9 7 2 6
Matters get more complicated if the number of entries in the array is not a multiple of the number of columns you want to use. For example,
A = randi([0 9], 1, 23)
A = 1×23
9 6 1 5 7 4 8 4 8 4 4 5 8 5 3 6 9 2 1 4 8 9 9
for K = 1 : 5 : numel(A); disp(A(K : min(end,K+4))); end
9 6 1 5 7 4 8 4 8 4 4 5 8 5 3 6 9 2 1 4 8 9 9

Jan on 5 Mar 2012
You can get help from the documentation of Matlab:
doc for
help for
There you find examples and explanations.
Meenakshi Bhardwaj on 19 Jul 2018
Thanks so much. Finally, I understood what is for loop.

Jan Afridi on 29 Sep 2017
For loop repeat itself for a given number of input. The syntax for “For Loop Matlab” is
for variable = expression
Program Statement
end
In the above syntax, the expression has one of the following forms.
Initial value : Final value
for x = 1:10
fprintf('value of x: %d\n', x);
end
Initial value : Step : Final value
for x = 1:2:10
fprintf('value of x: %d\n', x);
end
Value Array
for x = [1 4 6 8 90]
disp(x)
end

mohamed mohamed on 6 Feb 2021
Edited: Walter Roberson on 31 Jul 2021
for x = 1:10
fprintf('value of x: %d\n', x);
end
value of x: 1 value of x: 2 value of x: 3 value of x: 4 value of x: 5 value of x: 6 value of x: 7 value of x: 8 value of x: 9 value of x: 10

Narasimman P on 30 Jul 2021
for a=1:10
end
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Walter Roberson on 17 Nov 2021
The code posted by @Narasimman P is a completely valid for loop, just one that does not do anything inside the loop. All it does is count from 1 to 10 internally. After the loop, two things will have changed:
1. Time will have elapsed, which could be important if you are waiting for something to happen
2. The loop control variable 'a' will have the same value as it was last assigned, so in this case after the loop 'a' will have the double precision value 10 .
disp('before')
before
whos
disp('starting loop')
starting loop
for a=1:10
end
disp('after')
after
whos
Name Size Bytes Class Attributes a 1x1 8 double
So there has been output: the variable a did not exist before, and after the loop it does exist.

Manan Shah on 8 May 2022
Edited: Torsten on 8 May 2022
for i = 0:8 ;
a = pow10 (i);
disp a(i);
end
Walter Roberson on 8 May 2022
disp a(i)
would mean the same thing as
disp('a(i)')
You probably want
disp(a(i))

Iosif on 13 Nov 2022
Edited: Iosif on 13 Nov 2022
D=input ('Βαθος νερου σε m ')
W=input ('Βαρος ανα μοναδα μηκους της γραμμης αγκυρωσης στο νερο σε N/m ')
Hex=input ('εξωτερικη φορτηση σε kn ')
dx=input ('οριζοντια μετατοπιση σε m ')
if dx/D>=0.3 && dx/D<=0.6
else
disp ('Δωσε διαφορετικη τιμη για το dx')
dx=input ('οριζοντια μετατοπιση σε m ')
end
I want to make my programm go to if after else and run that lines again until if line is satisfied
Walter Roberson on 15 Nov 2022
while ~isnumeric(dx) || ~isscalar(dx) || dx/D<0.3 || dx/D>0.6
disp ('Δωσε διαφορετικη τιμη για το dx')
dx=input ('οριζοντια μετατοπιση σε m ')
end

Kartick on 11 Jan 2023 at 14:11
Edited: Kartick on 11 Jan 2023 at 14:13
There are 4 type of loops: while, for, if and case.
For loop :
Eg: you have your robot whom you wish to give command to walk 100steps. The command will be
for steps=1:100
end
disp(steps)
100
The robot will go 100steps and stop and output will be displayed as 100 after completion.
For loop is used to solve many mathematical problems like factorials etc.
Walter Roberson on 11 Jan 2023 at 18:48
Computer Scientists use the term "control statement" for code structures that will execute selectively exactly zero or one time. Computer Scientists use the term "loop" for code structures that have the potential to execute more than one time. "if" and "case" are control structures but are not loops.
If you imagine the execution point as starting from the "top" and falling downward, then "if" and "case" only ever have the execution point continuing to fall downwards, whereas "for" and "while" in general require pumping the execution point back up again.