if, elseif, else

Execute statements if condition is true

Syntax

if expression
statements
elseif expression
statements
else
statements
end

Description

example

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

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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

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.

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.

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');
end

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

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

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.

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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.