constrain()

Description

Constraints a number to be within a range. The input of this function could be, for example, a sensor value that controls a motor position, with the lower and upper ranges of the function being the physical limits of possible movement.

Syntax

Use the following function to constrain the range of a given variable:

constrain(x, a, b)

Parameters

The function admits the following parameters:

• x

  : the number to constrain. Allowed data types: all data types.

• a

  : the lower end of the range. Allowed data types: all data types.

• b

  : the upper end of the range. Allowed data types: all data types.

Returns

The function returns the following:

• x

  : if the input parameter (x) is between

  a

  and

  b

  .

• a

  : if the input parameter (x) is less than

  a

  .

• b

  : if the input parameter (x) is greater than

  b

  .

Example Code

The code sets an emulated sensor value and prints its constrained result on the Serial Monitor.

1int sensVal = 50;  // try with 170 and 5 to verify the functionality
2
3void setup() {
4  Serial.begin(9600);
5
6  sensVal = constrain(sensVal, 10, 150);  // limits range of sensor values between 10 and 150
7
8  Serial.print("The sensor value is: ");
9  Serial.println(sensVal);
10}
11
12void loop() {
13}

Notes and Warnings

Because of the way the

constrain()

This code will yield incorrect results:

1int constrainedInput = constrain(Serial.parseInt(), minimumValue, maximumValue);   // avoid this

Use this instead:

1int input = Serial.parseInt();  // keep other operations outside the constrain function
2int constrainedInput = constrain(input, minimumValue, maximumValue);

See also

• abs()
• map()
• max()
• min()
• pow()
• sq()
• sqrt