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The <= (less than or equal to) operator is a binary relational operator that compares two operands to determine if the value of the left operand is strictly less than or mathematically equal to the value of the right operand. 
operand1 <= operand2

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Return Value

In C, relational operators do not yield a distinct boolean type. The <= operator evaluates to an int. It returns 1 if the relation is true, and 0 if the relation is false.

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Operand Constraints and Type Promotion

The operator accepts operands of real arithmetic types (integer, character, and floating-point) or pointer types.
  • Arithmetic Operands: If the operands have different arithmetic types, the compiler applies the usual arithmetic conversions (implicit type promotion) to bring both operands to a common type before performing the comparison. For example, if comparing an int and a double, the int is promoted to a double.
  • Pointer Operands: Both operands must be pointers to compatible object or incomplete types. Pointer comparison evaluates the relative memory addresses.
    • Warning: Relational pointer comparison is strictly defined only when both pointers point to elements of the same array object, or one position past the last element of that array. Comparing pointers to distinct objects, or using a relational operator to compare a null pointer (even against another null pointer), results in undefined behavior.

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Precedence and Associativity

  • Precedence: The <= operator has lower precedence than arithmetic operators (like +, -, *, /) but higher precedence than equality operators (==, !=), logical operators (&&, ||), and assignment operators.
  • Associativity: It evaluates strictly from left to right.

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The Chaining Pitfall

Because of left-to-right associativity and the integer return type, chaining the <= operator is syntactically valid but rarely produces the mathematically expected result. 
a <= b <= c
The compiler evaluates this expression as (a <= b) <= c.
  1. a <= b is evaluated first, yielding an int of either 0 or 1.
  2. That resulting 0 or 1 is then compared against c (e.g., 1 <= c).
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