assignment of function c

How to Use Functions in C - Explained With Examples

Functions are an essential component of the C programming language. They help you divide bigger problems into smaller, more manageable chunks of code, making it simpler to create and run programs.

We'll look at functions in C, their syntax, and how to use them successfully in this article.

What is a Function in C?

A function is a block of code that executes a particular task in programing. It is a standalone piece of code that can be called from anywhere in the program.

A function can take in parameters, run computations, and output a value. A function in C can be created using this syntax:

The return_type specifies the type of value that the function will return. If the function does not return anything, the return_type will be void .

The function_name is the name of the function, and the parameter list specifies the parameters that the function will take in.

How to Declare a Function in C

Declaring a function in C informs the compiler about the presence of a function without giving implementation details. This enables the function to be called by other sections of the software before it is specified or implemented.

A function declaration usually contains the function name , return type , and the parameter types. The following is the syntax for defining a function in C:

Here, return_type is the data type of the value that the function returns. function_name is the name of the function, and parameter_list is the list of parameters that the function takes as input.

For example, suppose we have a function called add that takes two integers as input and returns their sum. We can declare the function as follows:

This tells the compiler that there is a function called add that takes two integers as input and returns an integer as output.

It's worth noting that function declarations do not include the function body, which includes the actual code that runs when the function is invoked.

The body of the function is defined independently of the function statement, usually in a separate block of code called the function definition.

Here's an example:

In this example, the add function is declared with a function statement at the top of the file, which specifies its name, return type ( int ), and parameters ( a and b , both int s).

The actual code for the add function is defined in the function definition. Here, the function simply adds its two parameters and returns the result.

The main function calls the add function with arguments 2 and 3 , and stores the result in the result variable. Finally, it prints the result using the printf function.

How to Use a Function in Multiple Source Files

If you want to use a function in numerous source files, you must include a function declaration (also known as a function prototype) in the header file and the definition in one source file.

when you build, you first compile the source files to object files, and then you link the object files into the final executable.

Let's create a header file called myfunctions.h :

In this header file, we declare a function add using a function statement.

Next, let's create a source file called myfunctions.c , which defines the add function:

In this file, we include the myfunctions.h header file using quotes, and we define the add function.

Finally, let's create a source file called main.c , which uses the add function:

In this file, we include both the stdio.h header file and our myfunctions.h header file using angle brackets and quotes, respectively. We then call the add function, passing in values a and b and storing the result in sum . Finally, we print the result using printf .

The way you create it is heavily influenced by your environment. If you are using an IDE (such as Visual Studio), you must position all files in the proper locations in the project.

If you are creating from the command line e.g Linux. To compile this program, you would need to compile both myfunctions.c and main.c and link them together as shown below:

The -c option instructs the compiler to create an object file with the same name as the source file but with a .o suffix. The final instruction joins the two object files to create the final executable, which is named program (the -o option specifies the name of the output file).

What Happens if You Call a Function Before Its Declaration in C?

In this instance, the computer believes the usual return type is an integer. If the function gives a different data type, it throws an error.

If the return type is also an integer, it will function properly. But some cautions may be generated:

In this code, the function function() is  called before it is declared. This returns an error:

How to Define a Function in C

Assuming you want to create a code that accepts two integers and returns their sum, you can define a function that does that this way:

In this example, the function sum takes in two integer parameters – num1 and num2 . The function calculates their sum and returns the result. The return type of the function is int .

Where Should a Function Be Defined?

In C, a function can be defined anywhere in the program, as long as it is defined before it is used. But it is a good practice to define functions at the beginning of the file or in a separate file to make the code more readable and organized.

Here's an example code showing how to define a function in C:

In this example, the function add() is defined after its declaration (or prototype) within the same file.

Another approach is to define the function in a separate header file, which is then included in the main file using the #include directive. For example:

In this approach, the function declaration (or prototype) is included in the header file math.h , which is then included in the main file main.c using the #include directive. The function implementation is defined in a separate file math.c .

This approach allows for better code organization and modularity, as the function implementation can be separated from the main program code.

How to Call a Function in C

We can call a function from anywhere in the program once we've defined it. We use the function name followed by the argument list in parentheses to call a function. For example, we can use the following code to call the sum function that we defined earlier:

In this code, we are calling the sum function with a and b as its parameters. The function returns the sum of a and b , which is then stored in the variable c .

How to Pass Parameters to a Function

There are two methods of passing parameters (also called arguments) to a function in C: by value and by reference.

When we pass a parameter by value, the method receives a copy of the parameter's value. Changes to the parameter within the code have no effect on the initial variable outside the function.

When we pass a parameter by reference, the method receives a link to the parameter's memory location. Any modifications to the parameter within the code will have an impact on the initial variable outside the function.

Consider the following examples of passing parameters by value and by reference. Assuming we want to create a function that accepts an integer and multiplies it by two, the function can be defined as follows:

In this example, the function doubleValue takes in an integer parameter num by value. It doubles the value of num and assigns it back to num . However, this change will not affect the original value of num outside the function.

Here's another example that shows how you can pass a single parameter by value:

In this example, we define a function called square that takes an integer parameter num by value. Inside the function, we calculate the square of num and print the result. We then call the function with the argument 5 .

Now, let's look at an example of passing a parameter by reference:

In this example, we define a function square that takes an integer pointer parameter num by reference. Inside the function, we reference the pointer and calculate the square of the value pointed to by num .

We then call the function with the address of the integer variable x . After calling the function, the value of x is modified to be the square of its original value, which we then print in the main function.

In conclusion, functions are an essential component of C programming. You can use them to divide large problems into smaller, more manageable pieces of code.

You can declare and define functions in C, and pass parameters either by value or by reference. It's a good practice to declare all functions before using them, and to define them at the beginning of the file or in a separate file for better code organization and modularity.

By using functions effectively, you can write cleaner, more readable code that is easier to debug and maintain.

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Next: Execution Control Expressions , Previous: Arithmetic , Up: Top   [ Contents ][ Index ]

7 Assignment Expressions

As a general concept in programming, an assignment is a construct that stores a new value into a place where values can be stored—for instance, in a variable. Such places are called lvalues (see Lvalues ) because they are locations that hold a value.

An assignment in C is an expression because it has a value; we call it an assignment expression . A simple assignment looks like

We say it assigns the value of the expression value-to-store to the location lvalue , or that it stores value-to-store there. You can think of the “l” in “lvalue” as standing for “left,” since that’s what you put on the left side of the assignment operator.

However, that’s not the only way to use an lvalue, and not all lvalues can be assigned to. To use the lvalue in the left side of an assignment, it has to be modifiable . In C, that means it was not declared with the type qualifier const (see const ).

The value of the assignment expression is that of lvalue after the new value is stored in it. This means you can use an assignment inside other expressions. Assignment operators are right-associative so that

is equivalent to

This is the only useful way for them to associate; the other way,

would be invalid since an assignment expression such as x = y is not valid as an lvalue.

Warning: Write parentheses around an assignment if you nest it inside another expression, unless that is a conditional expression, or comma-separated series, or another assignment.

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A function is a block of code that performs a specific task.

You will find examples related to functions in this article. To understand examples in this page, you should have the knowledge of the following topics:

• User-Defined Function
• Types of User-defined functions
• Scope of a local variable

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Assignment Operators in C

In C, the assignment operator stores a certain value in an already declared variable. A variable in C can be assigned the value in the form of a literal, another variable or an expression. The value to be assigned forms the right hand operand, whereas the variable to be assigned should be the operand to the left of = symbol, which is defined as a simple assignment operator in C. In addition, C has several augmented assignment operators.

The following table lists the assignment operators supported by the C language −

Simple assignment operator (=)

The = operator is the most frequently used operator in C. As per ANSI C standard, all the variables must be declared in the beginning. Variable declaration after the first processing statement is not allowed. You can declare a variable to be assigned a value later in the code, or you can initialize it at the time of declaration.

You can use a literal, another variable or an expression in the assignment statement.

Once a variable of a certain type is declared, it cannot be assigned a value of any other type. In such a case the C compiler reports a type mismatch error.

In C, the expressions that refer to a memory location are called "lvalue" expressions. A lvalue may appear as either the left-hand or right-hand side of an assignment.

On the other hand, the term rvalue refers to a data value that is stored at some address in memory. A rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Variables are lvalues and so they may appear on the left-hand side of an assignment. Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side. Take a look at the following valid and invalid statements −

Augmented assignment operators

In addition to the = operator, C allows you to combine arithmetic and bitwise operators with the = symbol to form augmented or compound assignment operator. The augmented operators offer a convenient shortcut for combining arithmetic or bitwise operation with assignment.

For example, the expression a+=b has the same effect of performing a+b first and then assigning the result back to the variable a.

Similarly, the expression a<<=b has the same effect of performing a<<b first and then assigning the result back to the variable a.

Here is a C program that demonstrates the use of assignment operators in C:

When you compile and execute the above program, it produces the following result −

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Copy assignment operator.

A copy assignment operator is a non-template non-static member function with the name operator = that can be called with an argument of the same class type and copies the content of the argument without mutating the argument.

[ edit ] Syntax

For the formal copy assignment operator syntax, see function declaration . The syntax list below only demonstrates a subset of all valid copy assignment operator syntaxes.

[ edit ] Explanation

The copy assignment operator is called whenever selected by overload resolution , e.g. when an object appears on the left side of an assignment expression.

[ edit ] Implicitly-declared copy assignment operator

If no user-defined copy assignment operators are provided for a class type, the compiler will always declare one as an inline public member of the class. This implicitly-declared copy assignment operator has the form T & T :: operator = ( const T & ) if all of the following is true:

• each direct base B of T has a copy assignment operator whose parameters are B or const B & or const volatile B & ;
• each non-static data member M of T of class type or array of class type has a copy assignment operator whose parameters are M or const M & or const volatile M & .

Otherwise the implicitly-declared copy assignment operator is declared as T & T :: operator = ( T & ) .

Due to these rules, the implicitly-declared copy assignment operator cannot bind to a volatile lvalue argument.

A class can have multiple copy assignment operators, e.g. both T & T :: operator = ( T & ) and T & T :: operator = ( T ) . If some user-defined copy assignment operators are present, the user may still force the generation of the implicitly declared copy assignment operator with the keyword default . (since C++11)

The implicitly-declared (or defaulted on its first declaration) copy assignment operator has an exception specification as described in dynamic exception specification (until C++17) noexcept specification (since C++17)

Because the copy assignment operator is always declared for any class, the base class assignment operator is always hidden. If a using-declaration is used to bring in the assignment operator from the base class, and its argument type could be the same as the argument type of the implicit assignment operator of the derived class, the using-declaration is also hidden by the implicit declaration.

[ edit ] Implicitly-defined copy assignment operator

If the implicitly-declared copy assignment operator is neither deleted nor trivial, it is defined (that is, a function body is generated and compiled) by the compiler if odr-used or needed for constant evaluation (since C++14) . For union types, the implicitly-defined copy assignment copies the object representation (as by std::memmove ). For non-union class types, the operator performs member-wise copy assignment of the object's direct bases and non-static data members, in their initialization order, using built-in assignment for the scalars, memberwise copy-assignment for arrays, and copy assignment operator for class types (called non-virtually).

[ edit ] Deleted copy assignment operator

An implicitly-declared or explicitly-defaulted (since C++11) copy assignment operator for class T is undefined (until C++11) defined as deleted (since C++11) if any of the following conditions is satisfied:

• T has a non-static data member of a const-qualified non-class type (or possibly multi-dimensional array thereof).
• T has a non-static data member of a reference type.
• T has a potentially constructed subobject of class type M (or possibly multi-dimensional array thereof) such that the overload resolution as applied to find M 's copy assignment operator
• does not result in a usable candidate, or
• in the case of the subobject being a variant member , selects a non-trivial function.

[ edit ] Trivial copy assignment operator

The copy assignment operator for class T is trivial if all of the following is true:

• it is not user-provided (meaning, it is implicitly-defined or defaulted);
• T has no virtual member functions;
• T has no virtual base classes;
• the copy assignment operator selected for every direct base of T is trivial;
• the copy assignment operator selected for every non-static class type (or array of class type) member of T is trivial.

A trivial copy assignment operator makes a copy of the object representation as if by std::memmove . All data types compatible with the C language (POD types) are trivially copy-assignable.

[ edit ] Eligible copy assignment operator

Triviality of eligible copy assignment operators determines whether the class is a trivially copyable type .

[ edit ] Notes

If both copy and move assignment operators are provided, overload resolution selects the move assignment if the argument is an rvalue (either a prvalue such as a nameless temporary or an xvalue such as the result of std::move ), and selects the copy assignment if the argument is an lvalue (named object or a function/operator returning lvalue reference). If only the copy assignment is provided, all argument categories select it (as long as it takes its argument by value or as reference to const, since rvalues can bind to const references), which makes copy assignment the fallback for move assignment, when move is unavailable.

It is unspecified whether virtual base class subobjects that are accessible through more than one path in the inheritance lattice, are assigned more than once by the implicitly-defined copy assignment operator (same applies to move assignment ).

See assignment operator overloading for additional detail on the expected behavior of a user-defined copy-assignment operator.

[ edit ] Example

[ edit ] defect reports.

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[ edit ] See also

• converting constructor
• copy constructor
• copy elision
• default constructor
• aggregate initialization
• constant initialization
• copy initialization
• default initialization
• direct initialization
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• zero initialization
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C Functions

C structures.

A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

Functions are used to perform certain actions, and they are important for reusing code: Define the code once, and use it many times.

Predefined Functions

So it turns out you already know what a function is. You have been using it the whole time while studying this tutorial!

For example, main() is a function, which is used to execute code, and printf() is a function; used to output/print text to the screen:

Create a Function

To create (often referred to as declare ) your own function, specify the name of the function, followed by parentheses () and curly brackets {} :

Example Explained

• myFunction() is the name of the function
• void means that the function does not have a return value. You will learn more about return values later in the next chapter
• Inside the function (the body), add code that defines what the function should do

Call a Function

Declared functions are not executed immediately. They are "saved for later use", and will be executed when they are called.

To call a function, write the function's name followed by two parentheses () and a semicolon ;

In the following example, myFunction() is used to print a text (the action), when it is called:

Inside main , call myFunction() :

A function can be called multiple times:

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Create a method named myFunction and call it inside main() .

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Assigning function to a variable in C++

In C++ , assigning a function to a variable and using that variable for calling the function as many times as the user wants, increases the code reusability. Below is the syntax for the same:

Program 1: Below is the C++ program to implement a function assigned to a variable:

Program 2: Below is the C++ program to implement a parameterized function assigned to a variable:

Program 3: Below is the C++ program to implement a function assigned to a variable that returns a value:

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