A Short C Program and A simple program Of C

This is a very simple program. All it does is input two numbers from the keyboard and calculate their product. At this stage, don't worry about understanding the details of the program's workings. The point is to gain some familiarity with the parts of a C program so that you can better understand the listings presented later in this book.
Before looking at the sample program, you need to know what a function is, because functions are central to C programming. A function is an independent section of program code that performs a certain task and has been assigned a name. By referencing a function's name, your program can execute the code in the function. The program also can send information, called arguments, to the function, and the function can return information to the main part of the program. The two types of C functions are library functions, which are a part of the C compiler package, and user-defined functions, which you, the programmer, create.

1:  /* Program to calculate the product of two numbers. */
2:  #include <stdio.h>
3:
4:  int a,b,c;
5:
6:  int product(int x, int y);
7:
8:  main()
9:  {
10:     /* Input the first number */
11:     printf("Enter a number between 1 and 100: ");
12:     scanf("%d", &a);
13:
14:     /* Input the second number */
15:     printf("Enter another number between 1 and 100: ");
16:     scanf("%d", &b);
17:
18:     /* Calculate and display the product */
19:     c = product(a, b);
20:     printf ("%d times %d = %d\n", a, b, c);
21:
22:     return 0;
23: }
24:
25: /* Function returns the product of its two arguments */
26: int product(int x, int y)
27: {
28:     return (x * y);
29: }

Enter a number between 1 and 100: 35
Enter another number between 1 and 100: 23
35 times 23 = 805