Declaring and calling a function in 'C' language

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Declaring and calling a function

/* program to find area of a ring */
#include<stdio.h>
float area();
float area2(float r);
int main() {
float a1,a2,a,r;
a1=area();
printf(“enter the radius:”);
scanf(“f”,&r);
a2=area2(r);
a=a1-a2;
prinf(“area of ring: %3f\n”,a);
}
float area() {
float r;
printf(“enter the radius:”);
scanf(“%f”,&r);
return(3.14*r*r);
}
float area2(float r) {
return(3.14*r*r);
}
But:
How is a function declared?
What is a function call?
What is a calling function?
What is a called function?

Declaration of a function (or) syntax of a function
return-value-type function-name (type parameter 1, type parameter 2, ... type parameter n)
{
definitions
statements
}
A function call is an expression that passes control and arguments (if any) to a function.
Functions are invoked by a function call, which specify the function name and provides information (as arguments) that the called function needs, to perform its designated task.
The function which receives control is called a called functions.
The function which sends control through a function call is called a calling function.
In the above program calling function is the main() and float area() and floatarea2() are the called functions.

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