Loop Control Statements
With loop control statements, you can repeatedly execute a block of code. There are two types of
loops:
• for statements loop a specific number of times, and keep track of each iteration with an
incrementing index variable.
For example, preallocate a 10-element vector, and calculate five values:
x = ones(1,10);
for n = 2:6
x(n) = 2 * x(n - 1);
end
• while statements loop as long as a condition remains true.
For example, find the first integer n for which factorial(n) is a 100-digit number:
n = 1;
nFactorial = 1;
while nFactorial < 1e100
n = n + 1;
nFactorial = nFactorial * n;
end
Each loop requires the end keyword.
It is a good idea to indent the loops for readability, especially when they are nested (that is, when one
loop contains another loop):
A = zeros(5,100);
for m = 1:5
for n = 1:100
A(m, n) = 1/(m + n - 1);
end
end
You can programmatically exit a loop using a break statement, or skip to the next iteration of a loop
using a continue statement. For example, count the number of lines in the help for the magic
function (that is, all comment lines until a blank line):
fid = fopen('magic.m','r');
count = 0;
while ~feof(fid)
line = fgetl(fid);
if isempty(line)
break
elseif ~strncmp(line,'%',1)
continue
end
count = count + 1;
end
fprintf('%d lines in MAGIC help\n',count);
fclose(fid);
Loop Control Statements
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