Basic function designs
Functions
are classified by their return values and their parameters list. Functions
either return a value or they don’t . Functions that don’t return a value are
called void functions. Combining return types and parameters list results in
the following designs:
Void functions without
parameters
Void functions with
parameters
Non-void functions
without parameters
No-void functions with
parameters
Void functions without
parameters:
We
can write a function without any parameters. Here, greeting function receives
nothing and returns nothing.
//function
declaration
void
greeting(void);
int
main(void)
{
//
statements
greeting();
//call
return
0;
}
//main
void
greeting(void)
{
print(“hello
world:”);
return;
}
//greeting
If
the void function does not have a value, it can be used only as a statement; it
cannot be used in an expression.
Void functions with parameters:
Let’s
call a function that has parameters but still returns void. Since this function
returns nothing to the functions, main, its return type is void.
//function
declaration
void
printone(int x);
int
main(void)
{
//local
declarations
int
a=5;
//statements
printone(a);
//call
return
0;
}
//main
void
printone(void)
{
printf(“%d\n”,x);
return;
}
//printone
Non-void functions
without parameters:
Some
functions don’t have any parameters but return a value.
//function
declaration
int
getquantity(void);
int
main(void)
{
//local
declaration
int
amt;
//statements
amt
= getquantity();
...
return
();
}
//main
int
getquantity(void);
{
//local
declaration
int
qty;
//statements
printf(“Enter
quantity”);
scanf(“%d”,&qty);
return
qty;
}
//getquantity
The
most common use for this design reads data from the keyboard or a file and
returns the data to the calling program.
Non-void functions
with parameters:
The
program contains a function that passes parameters and returns a value. Here,
square of the parameter is the function. The returned value is place in the
variable b, as shown. This is done by the result of expression evaluation and
not by the call.
//function
declaration
int
sqr(int x);
int
main(void);
{
//local
declaration
int
a;
int
b;
//statements
scanf(“%d\n”,&a);
b=sqrt(a);
printf(“%d\n”,a,b);
return
0;
}
//main
int
sqr(int x);
{
//statements
return(x
* x);
}
//sqr
x
