C Tutorials
| Functions in C |
A function is a group of statements that together perform a task. Every C program has at least one function which is main(), and all the most trivial programs can define additional functions. We can divide up your code into separate functions.
A function declaration tells the compiler about a function's name, return type, and parameters. A function definition provides the actual body of the function. The C standard library provides numerous built-in functions that your program can call. For example, function strcat() to concatenate two strings, function memcpy() to copy one memory location to another location and many more functions. A function is known with various names like a method or a sub-routine or a procedure etc.
| Defining a Function |
return_type function_name(parameter_list)
{
body of function
}
A function definition in C programming language consists of a function header and a function body. Here are all the parts of a function:
Return Type: A function may return a value. The return_type is the data type of the value the function returns. Some functions perform the desired operations without returning a value. In this case, the return_type is the keyword void.
Function Name: This is the actual name of the function. The function name and the parameter list together constitute the function signature.
Parameters: A parameter is like a placeholder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters.
Function Body: The function body contains a collection of statements that define what the function does.
int max(int num1, int num2)
{
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
| Function Declaration |
A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately.
return_type function_name (parameter_list);
int max(int num1, int num2);
| Calling a Function |
When a program calls a function, program control is transferred to the called function. A called function performs defined task and when its return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program.
To call a function you simply need to pass the required parameters along with function name and if function returns a value then you can store returned value. For example:
#include <stdio.h>
int max(int num1, int num2);
int main ()
{
int a = 100;
int b = 200;
int m;
m = max(a, b);
printf( "Max value is : %d\n", m );
return 0;
}
int max(int num1, int num2)
{
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
| Function Arguments |
While calling a function, there are two ways that arguments can be passed to a function. By default, C uses call by value to pass arguments.
| Call Type | Description |
|---|---|
| Call by value | This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument. |
| Call by reference | This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. |
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