Dynamic Evaluation & Timing

eval — string execution

eval(str) executes a string as ccalc code in the current workspace. Variables defined inside the string persist in the caller’s scope, matching MATLAB/Octave semantics.

eval('x = sqrt(2)')    % x is now defined in the workspace
x                      % → 1.4142…

eval('disp(pi)')       % prints 3.14159…

Dynamic variable naming

A common idiom is building variable names at runtime with sprintf:

for k = 1:3
  eval(sprintf('v%d = k*k', k))
end
v1    % → 1
v2    % → 4
v3    % → 9

Two-argument form — catching errors

eval(try_str, catch_str) executes catch_str if try_str raises an error. The original error message is available via lasterr() inside the catch string.

eval('error(''oops'')', 'fprintf(''caught: %s\n'', lasterr())')

eval in expression context

When eval is used on the right-hand side of an assignment, it returns ans from the inner execution. Variable mutations inside do not propagate back to the caller’s workspace.

y = eval('2 + 2')    % y = 4

Nesting

eval calls can be nested. The depth limit is 64 (shared with run/source).

tic / toc — elapsed time

tic starts (or restarts) a timer. toc reads the elapsed time in seconds since the last tic.

tic
A = rand(500) * rand(500);
t = toc                           % → e.g. 0.0042  (seconds)

tic
for k = 1:1000
  x = k^2;
end
fprintf('loop: %.4f s\n', toc)

Both tic and toc can be written with or without parentheses:

tic
t = toc
% same as
tic()
t = toc()

Multiple toc calls after a single tic are valid — the timer is not reset by toc. Calling toc before any tic is an error.

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