Macro with arguments - Step-by-Step Execution

Concept Flow - Macro with arguments

Define macro with args

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Use macro in code

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Preprocessor replaces macro call

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Code compiles with replaced text

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Program runs with macro effect

A macro with arguments is defined and then used in code; the preprocessor replaces the macro call with the expanded code before compilation.

Execution Sample

C

#define SQUARE(x) ((x) * (x))
int main() {
  int a = 5;
  int b = SQUARE(a);
  return b;
}

This code defines a macro SQUARE that calculates the square of a number and uses it to compute b = 25.

Execution Table

Step	Code Line	Macro Expansion	Variable Values	Action
1	#define SQUARE(x) ((x) * (x))	Macro defined	-	Macro SQUARE with argument x is defined
2	int a = 5;	-	a=5	Variable a initialized to 5
3	int b = SQUARE(a);	int b = ((a) * (a));	a=5, b=25	Macro call replaced by ((a) * (a)), b computed as 25
4	return b;	-	b=25	Return value is 25
5	Program ends	-	-	Program ends with return 25

💡 Program ends after returning b=25, macro expansion done before compilation

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
a	undefined	5	5	5
b	undefined	undefined	25	25

Key Moments - 2 Insights

Why does the macro use extra parentheses around (x) and the whole expression?

Parentheses ensure correct order of operations when the macro argument is an expression; see Step 3 where ((a) * (a)) prevents errors if x is complex.

Is the macro a function? Does it evaluate its argument multiple times?

No, it's a text replacement done before compilation. The argument x is repeated twice in the expansion, so if x has side effects, it runs twice. See Step 3 macro expansion.

Visual Quiz - 3 Questions

Look at the execution table at Step 3, what is the value of b after macro expansion?

A 5

B 25

C 10

D Undefined

💡 Hint

Check the 'Variable Values' column at Step 3 in the execution table

At which step is the macro SQUARE actually replaced by its code?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Macro Expansion' column to see where replacement happens

If we change the macro to #define SQUARE(x) (x * x) without parentheses, what problem might occur?

A No problem, works same

B Compilation error

C Wrong calculation if x is an expression like a+1

D Macro won't expand

💡 Hint

Think about operator precedence and how parentheses affect the expanded code

Concept Snapshot

#define MACRO_NAME(args) replacement
Macro with arguments replaces calls with code using those args.
Use parentheses around args and whole expression to avoid errors.
Macro is text substitution done before compilation.
Beware: arguments may be evaluated multiple times.

Full Transcript

This example shows how a macro with arguments works in C. First, the macro SQUARE is defined to compute the square of a value. When the program runs, the macro call SQUARE(a) is replaced by ((a) * (a)) before compilation. Variable a is set to 5, then b is assigned the result of the macro expansion, which is 25. The program returns 25. Parentheses in the macro ensure correct calculation even if the argument is complex. The macro is not a function; it is a text replacement, so arguments can be evaluated multiple times if used more than once in the macro body.