Get free ebooK with 50 must do coding Question for Product Based Companies solved
Fill the details & get ebook over email
Thank You!
We have sent the Ebook on 50 Must Do Coding Questions for Product Based Companies Solved over your email. All the best!

What is a Function Prototype?

In this article, we will learn about a function prototype. It is a crucial part of C programming and other languages, as they provide a way to declare the functions before they are actually defined. Let us discuss the function prototype in detail.

Function Prototype

A function prototype is a declaration of a function that describes the function’s interface to the compiler. It provides information about the function’s name, return type, and the number and types of arguments that the function takes. The function prototype is usually placed at the beginning of a source file or in a header file, and it allows the compiler to check the function’s usage throughout the program. This can help to catch errors early on and improve the efficiency of the compilation process.

Syntax of function prototype:

return_type function_name (parameter_list);

Explanation of syntax of function prototype:
Here, ‘return_type’ is the data type of the value that the function will return, ‘function_name’ is the name of the function, and ‘parameter_list’ is a comma-separated list of the input parameters that the function will accept.

Example for Function Prototype

Below is an example of a function prototype-

#include <stdio.h>

// Function prototype
int add(int a, int b);

int main() {
    int num1 = 5, num2 = 10, sum;
    sum = add(num1, num2);
    printf("The sum of %d and %d is %d\n", num1, num2, sum);
    return 0;

// Function definition
int add(int a, int b) {
    return a + b;


The result of 5 and 10 is 15

Explanation for function prototype:
In this program, we have declared a function prototype for the add function before the main function. This tells the compiler that there is a function named add that takes two int arguments and returns an int. Later the main function, will calls add with two integer arguments and assign the result to a variable sum, which we then print to the console using printf.

Difference between Function Prototype and Function Definition

The difference between a function prototype and a function declaration are

Function Prototype Function Definition
1. The function prototype includes the function name, return type, and parameters but does not include the function body. 1. The function definition includes the function name, return type, and parameters, as well as the function body.
2. The function implementation is not present in the function prototype. 2. The function implementation is included in the function definition.
3. Typically appears at the top of a source file or in a header file. 3. Typically appears below the prototype in a source file.
4. Used to enable the compiler to verify the function’s usage and type-checking during compilation. 4. Used to enable the linker to create the executable code that can be executed by the computer.

Function Prototype for Scope and Conversion

The scope of the function prototype is determined by its position in the program. The scope of the function prototype is determined by its position in the program. If it is stated within the same block as the function call, any surrounding block, or at the source file’s outermost level, it is considered within the scope of a matching function call.

An argument is a value defined within the function that is passed to a function when it is called. They are used in function call statements to transfer data from the calling function to the calling function’s destination function. As an outcome, when we call a function, we must provide parameters of the same data type that was specified in the function prototype. When we call a function with arguments of different data types than those specified in the function declaration, argument conversion occurs. This is also made easier by the use of function prototypes.

In the function prototype of the standard math library function sqrt, for example, there is a double-type argument. It can, however, be called with an integer parameter and work perfectly fine.

Example for Function Prototype for Scope and Conversion:

using namespace std;
int main() {
   int n=25;
   int res = sqrt(n);
   cout<< res;
   return 0;



Explanation for Function Prototype for Scope and Conversion:
In this program, we have taken the value of n and also a variable name result to store the value of sqrt of n then output the value.

Advantages of Function Prototype

Some advantages of function prototype are:

  • It can help prevent run-time errors and improve program reliability.
  • This can help other programmers quickly understand how to use the function without having to read the entire code.
  • It modularizes the code by separating the function’s declaration from its implementation.
  • While debugging a program, function prototypes help identify where the problem occurred and speed up the debugging process.

Disadvantages of Function Prototype

Some disadvantages of function prototype are:

  • Function prototypes only provide limited information.
  • Maintaining and updating function prototypes can be time-consuming.
  • Function prototypes can lead to duplicated effort when defining function signatures.
  • Mismatched function prototypes and definitions can cause errors.
  • Function prototypes can increase code size and impact performance.

The purpose of function prototypes is to enable the compiler to check that function calls in the code match the function’s definition. This ensures that the correct number and types of arguments are passed to the function and that the function’s return type matches the expected type. In addition to providing type checking, function prototypes also make it easier for other programmers to understand the interface of the function. By looking at the prototype, they can quickly see what the function does, what parameters it expects, and what it returns. Overall, function prototypes are an important part of C programming, helping to ensure type safety and code correctness while also making code more readable and maintainable.

Frequently Asked Questions(FAQs)

1. In C++, what do functions prototypes mean?
In the C++ programming language, function prototypes are used to provide function declaration. It specifies the name of the function, as well as its return types and parameters. The return types are the data types returned by the function after execution. The return type of a function that returns an integer is int.

2. Why use a function prototype in C++?
The function prototypes are used to inform the compiler about the number of arguments and the required datatypes of a function parameter, as well as the function’s return type. The compiler uses this information to cross-check function signatures before calling them.

3. In C++ syntax, what is a function prototype?
In C++, Function Prototype is a function declaration that informs the program about the function’s number and type of parameters, as well as the type of value it will return.

4. What is the difference between a function prototype and a definition?
The main difference between the function prototype and the function definition is that the function prototype only contains the function’s declaration, whereas the function definition includes the function’s actual implementation.

5. Is a function prototype required in C++?
A prototype is also a declaration. I use static functions within a module without declaring or prototyping them. It should be noted that this has nothing to do with class methods. As a result, C++ does not require function declaration/prototyping

Leave a Reply

Your email address will not be published. Required fields are marked *