Lesson 8.2. Calling C functions

Syntax

Calling a function is done simply by specifying the name of the function followed by the parameters in parentheses:

x = max (4,3);

The parameters can be:

a value ;
a calculation;
a symbolic constant; *
a variable
a call to a function.

It is possible to mix the parameters as long as they respect the types declared in the prototype:

#define N 10

int max(int a, int b);

int main(void)
{
  float x,y=2,z=18;
  x = max (5,26);         // Values
  x = max(y,z);           // Variables
  x = max(y,N);           // Variables and constant
  x = max (max(y,z), 10); // Function and value

  if (max(y,z) > 10) {    // Variables in a test
    ...
  }
  ...
}

The parentheses

The call to a function is always followed by parentheses to differentiate the function from variables with the same name. Let's analyze the following example:

int name (void) {
  int name=26;
  return name;
}

The above code implements a function name() that contains a variable also called name. When name is followed by parentheses, it is the function, otherwise the variable. Without the parentheses, the compiler cannot differentiate the variable name from the function name(). Parentheses are always added after the name of a function, even in text or comments. Of course, this type of code should be avoided to prevent confusion.

Try online

Exercise

Write a function average() that returns the average of three floating-point numbers. Test your function with a main program that asks the user to enter three values before displaying the average. The average() function should not display anything, but return the result of the calculation to the main program.

Enter the first value: 12.4
Enter the second value: 13.7
Enter the third value: 10.2
-----------------------
The average is 12.10

Do the exercise

Solution

Quiz

The call of the function ...

can appear several times in the code

is necessarily made from the main program

can be done from another function

must have the same number of arguments as the prototype

Check

When calling a function, the parameters can be ...

a constante

a variable

call to another function

call the the same function

Check

Let's consider the following function, which calls are valid?

int max (int a, int b);

x = max 2,3;

x = max (2,3,4);

x = max (2,3);

x = max (2.1);

Check

Let's consider a function max() that returns the larger of two integers. What does the following code display?

int x;
x = max( 10, max (5,12));
printf ("%d", x );

The code does not compile

Check

Lesson 8.1 Summary Lesson 8.3

Lesson 8.2. Calling C functions

Syntax

The parentheses

Exercise

Quiz

See also