Differences Between Formal Arguments and Actual Arguments of a Function

Argument: An argument is an expression which is passed to a function by its caller (or macro by its invoker) in order for the function(or macro) to perform its task. It is an expression in the comma-separated list bound by the parentheses in a function call expression.

Actual arguments:

The arguments that are passed in a function call are called actual arguments. These arguments are defined in the calling function.

Formal arguments:

The formal arguments are the parameters/arguments in a function declaration. The scope of formal arguments is local to the function definition in which they are used. Formal arguments belong to the called function. Formal arguments are a copy of the actual arguments. A change in formal arguments would not be reflected in the actual arguments.

Example:

#include <stdio.h>

void sum(int i, int j, int k);

/* calling function */

int main() {

int a = 5;

// actual arguments

sum(3, 2 * a, a);

return 0;

}

/* called function */

/* formal arguments*/

void sum(int i, int j, int k) {

int s;

s = i + j + k;

printf("sum is %d", s);

}

Here 3,2*a,a are actual arguments and i,j,k are formal arguments.