Categories of user-defined functions
All C functions can be called either with arguments or without arguments in a C program. Also, they may or may not return any values.
A function depending on whether arguments are present or not and whether value is returned or not, may belong to one of the following categories:
Function with no arguments and no return value
Function with no arguments and a return value
Function with arguments and no return value
Function with arguments and a return value
Function with no arguments and no return value
When a function has no arguments, it does not receive any data from the calling function. Similarly when it does not return a value, the calling function does not receive any data from the called function.
Syntax:
Function declaration : void function();
Function call : function();
Function definition :
void function()
{
//statements;
}
Below is an example of a function, which takes 2 numbers as input from user, and display which is the greater number.
#include<stdio.h>
void greatNum(); // function declaration
int main()
{
greatNum(); // function call
return 0;
}
void greatNum() // function definition
{
int i, j;
printf("Enter 2 numbers that you want to compare...");
scanf("%d%d", &i, &j);
if(i > j) {
printf("The greater number is: %d", i);
}
else {
printf("The greater number is: %d", j);
}
}
Output:
Enter 2 numbers that you want to compare...
10 20
The greater number is: 20
Function with no arguments and a return value
There could be occasions where we may need to design functions that may not take any arguments but return a value to the calling function.
An example for this is getchar() function it has no parameters but it returns an integer type data that represents a character.
Syntax:
Function declaration: return_type function ();
Function call: function();
Function definition:
return_type function( ) {
//statements;
return x;
}
Below is an example of a function with no arguments but have return value
// C code for function with no arguments
// but have return value
#include<stdio.h>
int greatNum(); // function declaration
int main()
{
int r = greatNum(); // function call
printf("The greater number is: %d", r);
return 0;
}
int greatNum() // function definition
{
int i, j;
printf("Enter 2 numbers that you want to compare...");
scanf("%d%d", &i, &j);
if(i > j)
return i;
else
return j;
}
Output:
Enter 2 numbers that you want to compare...
10
20
The greater number is: 20
Function with arguments and no return value
When a function has arguments, it receives data from the calling function but it returns no values.
Syntax:
Function declaration :
void function (data_type arg1,data_type arg2,.. );
Function call :
function(arg1,arg2,.. );
Function definition:
void function(data_type arg1,data_type arg2,.. )
{
statements;
}
Below is an example of a function with arguments but no return value
// C code for function with arguments
// and no return value
#include<stdio.h>
void greatNum(int,int); // function declaration
int main()
{
int i, j;
printf("Enter 2 numbers that you want to compare...");
scanf("%d%d", &i, &j);
greatNum(i,j); // function call
return 0;
}
void greatNum(int n1,int n2) // function definition
{
if(n1 > n2)
printf("The greater number is: %d", n1);
else
printf("The greater number is: %d", n2);
}
Output:
Enter 2 numbers that you want to compare...
10 20
The greater number is: 20
Function with arguments and a return value
Syntax:
Function declaration :
int function (data_type arg1,data_type arg2,..);
Function call :
function( arg1, arg2,.. );
Function definition:
return_type function(data_type arg1,data_type arg2,.. )
{
statements;
return x;
}
Below is an example of a function with arguments and return value
// C code for function with arguments
// and return value
#include<stdio.h>
int greatNum(int,int); // function declaration
int main()
{
int i, j, r;
printf("Enter 2 numbers that you want to compare...");
scanf("%d%d", &i, &j);
r = greatNum(i,j); // function call
printf("The greater number is: %d", r);
return 0;
}
int greatNum(int n1,int n2) // function definition
{
if(n1 > n2)
return n1;
else
return n2;
}
Output:
Enter 2 numbers that you want to compare...
10
20
The greater number is: 20
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