3.6. Definitions and Uses

Pulling together all the code fragments from the previous section, the whole program looks like this:

#include <iostream> void new_line () { std::cout << '\n'; } void three_line () { new_line (); new_line (); new_line (); } int main () { std::cout << "First Line.\n"; three_line (); std::cout << "Second Line.\n"; return 0; }

This program contains three function definitions: new_line, three_line, and main.

Inside the definition of main, there is a statement that uses or calls three_line. Similarly, three_line calls new_line three times. Notice that the definition of each function appears above the place where it is used.

This is necessary in C++; the declaration or definition of a function must appear before (above) the first use of the function. It is possible for only the declarations for appear before a function is used and for the definition to appear later. These are called forward declarations.

#include <iostream> // forward declarations void new_line (); void three_line (); int main () { std::cout << "First Line.\n"; three_line (); std::cout << "Second Line.\n"; return 0; } void new_line () { std::cout << '\n'; } void three_line () { new_line (); new_line (); new_line (); }

Try This!

You should try compiling both programs with the functions in a different order and see what error messages you get.

Q-3: The function declaration or definition must be written the first use of the function.

Q-4: Which of the following is a correct function declaration?

• void print_name()

• This declaration is missing a ;.

• total_cost_after_tax () {

• This declaration is missing a return type.

• void todays_weather ();

• Correct!

• void final_grade {

• This declaration is missing parentheses. Even if a function does not take in any parameters, empty parentheses should be used.

Construct a block of code that correctly defines a the add_two function.

        int add_two(int x) {

int add_two(int x); #distractor

add_two(int x) #distractor

int add_two(int x) #distractor

 int new = x + 2;

 return new;

 return x; #distractor

}
        

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More to Explore

• From cppreference.com

  • Function definitions and declarations

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