User-defined functions are functions that are created by the programmer rather than being part of the C++ standard library. They are created using the keyword function.
A user-defined function can be used to perform any type of operation that can be performed in a program. For example, it can perform calculations, input and output operations, or any other type of operation that you can imagine.
Here is an example of a user-defined function in C++:
#include <iostream>
int add(int a, int b) {
return a + b;
}
int main() {
int x = 2, y = 3;
int sum = add(x, y);
std::cout << "The sum of " << x << " and " << y << " is " << sum << std::endl;
return 0;
}
In this example, the function add takes two integers as input, performs the operation of adding them, and returns the result. This function is called in the main function, passing the variables x and y as input parameters, and assigns the returned value to the variable sum. The output will be "The sum of 2 and 3 is 5".
User-defined functions can have any valid C++ data type as return type, including void, and can take any number of input parameters, including none. They can also have default values for the input parameters, which can be omitted when the function is called.
User-defined functions are useful for several reasons:
1. They help to organize and structure a program by breaking it down into smaller, more manageable parts.
2. They allow for code reuse by encapsulating a specific piece of functionality in one place, and can be called from multiple places in a program.
3. They make it easier to test and debug a program by isolating specific functionality in a separate function.
4. They can also improve the readability of the code.
5. They can also help to reduce code duplication.
User-defined functions can be defined anywhere in the code, but it's a good practice to put the function before the main function, or in a separate file with a header file.
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