if/elseif/else - Execute statements if condition is true

Syntax

if expression
   statements
elseif expression
   statements
else
   statements
end

Description

if expression, statements, end evaluates an expression, and executes a group of statements when the expression is true.

elseif and else are optional, and execute statements only when previous expressions in the if block are false. An if block can include multiple elseif statements.

An evaluated expression is true when the result is nonempty and contains all nonzero elements (logical or real numeric). Otherwise, the expression is false.

Expressions can include relational operators (such as < or ==) and logical operators (such as &&, ||, or ~). MATLAB evaluates compound expressions from left to right, adhering to operator precedence rules.

Tips

• You can nest any number of if statements. Each if statement requires an end keyword.

• Avoid adding a space within the elseif keyword (else if). The space creates a nested if statement that requires its own end keyword.

• Within an if or while expression, all logical operators, including | and &, short-circuit. That is, if the first part of the expression determines a true or false result, MATLAB does not evaluate the second part of the expression.

Examples

Assign to a matrix values that depend on their indices:

% Preallocate a matrix
nrows = 10;
ncols = 10;
myData = ones(nrows, ncols);

% Loop through the matrix
for r = 1:nrows
   for c = 1:ncols

      if r == c
         myData(r,c) = 2;
      elseif abs(r - c) == 1
         myData(r,c) = -1;
      else
         myData(r,c) = 0;
      end

   end
end

Respond to command-line input. Because the input string could be more than one character, use strcmp rather than == to test for equality:

reply = input('Would you like to see an echo? (y/n): ', 's');
if strcmp(reply,'y')
  disp(reply)
end

Find the indices of values in a vector that are greater than a specified limit:

A = rand(1,10);
limit = .75;

B = (A > limit);   % B is a vector of logical values
if any(B)
  fprintf('Indices of values > %4.2f: \n', limit);
  disp(find(B))
else
  disp('All values are below the limit.')
end

Concatenate two variables when they are the same size. To avoid an error when the variables have different dimensions, compare the sizes using isequal rather than the == operator:

A = ones(2,3);            % Two-dimensional array
B = rand(3,4,5);          % Three-dimensional array

if isequal(size(A), size(B))
   C = [A; B];
else
   warning('A and B are not the same size.');
   C = [];
end

Take advantage of short-circuiting to avoid error or warning messages:

x = 42;
if exist('myfunction.m') && (myfunction(x) >= pi)
   disp('Condition is true')
end

See Also

for | return | switch | while

Tutorials

• Relational Operators
• Logical Operators