C Programming
In this tutorial we will learn about the basic structure of a C program.
Following is the basic structure of a C program.
main()
Lets explore the sections with an example.
In the following example we will find the area of a circle for a given radius 10cm.
The formula to compute the area of a circle is πr2 where π is PI = 3.1416 (approx.) and r is the radius of the circle.
πr2
π
r
Lets write the C code to compute the area of the circle.
/** * file: circle.c * author: yusuf shakeel * date: 2010-11-25 * description: program to find the area of a circle * using the radius r */ #include <stdio.h> #define PI 3.1416 float area(float r); int main(void) { float r = 10; printf("Area: %.2f", area(r)); return 0; } float area(float r) { return PI * r * r; }
The above code will give the following output.
Area: 314.16
This section contains a multi line comment describing the code.
/** * file: circle.c * author: yusuf shakeel * date: 2010-11-25 * description: program to find the area of a circle * using the radius r */
In C, we can create single line comment using two forward slash // and we can create multi line comment using /* */.
//
/* */
Comments are ignored by the compiler and is used to write notes and document code.
This section includes header file.
#include <stdio.h>
We are including the stdio.h input/output header file from the C library.
stdio.h
This section contains constant.
#define PI 3.1416
In the above code we have created a constant PI and assigned 3.1416 to it.
The #define is a preprocessor compiler directive which is used to create constants. We generally use uppercase letters to create constants.
#define
The #define is not a statement and must not end with a ; semicolon.
;
This section contains function declaration.
float area(float r);
We have declared an area function which takes a floating number (i.e., number with decimal parts) as argument and returns floating number.
area
This section contains the main() function.
int main(void) { float r = 10; printf("Area: %.2f", area(r)); return 0; }
This is the main() function of the code. Inside this function we have created a floating variable r and assigned 10 to it.
Then we have called the printf() function. The first argument contains "Area: %.2f" which means we will print floating number having only 2 decimal place. In the second argument we are calling the area() function and passing the value of r to it.
printf()
"Area: %.2f"
area()
This section contains a subprogram, an area() function that is called from the main() function.
float area(float r) { return PI * r * r; }
This is the definition of the area() function. It receives the value of radius in variable r and then returns the area of the circle using the following formula PI * r * r.
PI * r * r