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

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

Examples

Use if, elseif, and else for Conditional Assignment

Create a matrix of 1s.

nrows = 4;
ncols = 6;
A = ones(nrows,ncols);

Loop through the matrix and assign each element a new value. Assign 2 on the main diagonal, -1 on the adjacent diagonals, and 0 everywhere else.

for c = 1:ncols
    for r = 1:nrows
        
        if r == c
            A(r,c) = 2;
        elseif abs(r-c) == 1
            A(r,c) = -1;
        else
            A(r,c) = 0;
        end
        
    end
end
A

A = 4×6

     2    -1     0     0     0     0
    -1     2    -1     0     0     0
     0    -1     2    -1     0     0
     0     0    -1     2    -1     0

Compare Arrays

Expressions that include relational operators on arrays, such as A > 0, are true only when every element in the result is nonzero.

Test if any results are true using the any function.

limit = 0.75;
A = rand(10,1)

A = 10×1

    0.8147
    0.9058
    0.1270
    0.9134
    0.6324
    0.0975
    0.2785
    0.5469
    0.9575
    0.9649

if any(A > limit)
    disp('There is at least one value above the limit.')
else
    disp('All values are below the limit.')
end

There is at least one value above the limit.

Test Arrays for Equality

Compare arrays using isequal rather than the == operator to test for equality, because == results in an error when the arrays are different sizes.

Create two arrays.

A = ones(2,3);
B = rand(3,4,5);

If size(A) and size(B) are the same, concatenate the arrays; otherwise, display a warning and return an empty array.

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

A and B are not the same size.

Compare Character Vectors

Use strcmp to compare character vectors. Using == to test for equality results in an error when the character vectors are different sizes.

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

Test Values for Inequality

Determine if a value is nonzero. Use the ~= operator to test for inequality.

x = 10;
if x ~= 0
    disp('Nonzero value')
end

Nonzero value

Evaluate Multiple Conditions in Expression

Determine if a value falls within a specified range.

x = 10;
minVal = 2;
maxVal = 6;

if (x >= minVal) && (x <= maxVal)
    disp('Value within specified range.')
elseif (x > maxVal)
    disp('Value exceeds maximum value.')
else
    disp('Value is below minimum value.')
end

Value exceeds maximum value.

More About

Expression

An expression can include relational operators (such as < or ==) and logical operators (such as &&, ||, or ~). Use the logical operators and and or to create compound expressions. MATLAB^® evaluates compound expressions from left to right, adhering to operator precedence rules.

Within the conditional expression of an if...end block, logical operators & and | behave as short-circuit operators. This behavior is the same as && and ||, respectively. Since && and || consistently short-circuit in conditional expressions and statements, it is good practice to use && and || instead of & and | within the expression. For example,

x = 42;
if exist('myfunction.m','file') && (myfunction(x) >= pi)
    disp('Expressions are true')
end

The first part of the expression evaluates to false. Therefore, MATLAB does not need to evaluate the second part of the expression, which would result in an undefined function error.

Tips

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

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

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

• Do not use the & and | operators within conditions of an if statement. Instead, use the && and || operators.

• HDL Coder™ does not support nonscalar expressions in the conditions of if statements. Instead, use the all or any functions to collapse logical vectors into scalars.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a