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Comma Operator in C

The comma operator in C is used to separate two or more expressions, evaluating them from left to right. The value of the entire expression is the value of the last expression.

Syntax

expression1, expression2, ..., expressionN;

Example

int a, b, c; c = (a = 5, b = 10, a + b); // a is 5, b is 10, c is 15

How it Works

  • All expressions separated by commas are evaluated in order from left to right
  • Only the value of the last expression is returned
  • Useful when multiple expressions need to be executed in a single statement

Use Cases

  • Inside for loops to update multiple variables: for(i=0, j=10; i
  • Combining multiple expressions in a single assignment
  • Executing multiple function calls in a single statement

Common Mistakes

  • Confusing comma operator with comma in function arguments (they are different)
  • Overusing in complex expressions reduces readability
  • Assuming all expressions return a value (only the last one matters)
  • Using outside of context where sequential evaluation is needed