CSCI 130

Chapter 2

Program Components

• main()• #include• Variable Definition• Function Prototype• Program Statements• Function Call• Function Definition• Comments

main()

• Required in every program– Under normal circumstances:

• program starts at first statement in main

• program ends at last statement in main

– Ex:• void main() {

• printf(“Hello World”);

• }

#include

• Instructs C compiler to add contents of another file during compilation

• #include statements at top of file

• Usually called header files (.h)– Some supplied with compiler

• Never modified

– Some user defined• Can be modified

Example of #include

• Library function– #include <stdio.h>– greater than, less than indicate library function

• User defined function– #include “myfile.h”– quotation marks indicate user-defined function– if not in same directory as main file, need to

specify the path

Variable Definition

• Variable - name assigned to a data storage location

• Must define a variable before it can be used

• Definition informs compiler of:– variable name– type of data

• Ex:– int a;– char a, b, c;

Program Statements

• These statements do the ‘Real’ work

• One per line, end with semi-colon

• Statements perform various functions:– input/output

• write to screen/file/printer• accept from screen/file

– call functions– perform calculations– other

The Function Call

• ‘Calling a function’– asking compiler to execute a function outside of

the main() function

• Ex:– printf(“Hello World”);– doReset()– c = product(a,b)

Function Definition

• A function:

• is a self contained block of code

• performs a specific task

• A function may be:– a library function

• printf()

– a user defined function• doMultiply()

Example of a function, and a function call

• Function:• int doMultiply(int x, int y) {

• return(x*y);

• }

• Function call:• ...programming statements…

• c = doMultiply(3,6);• …programming statements...

Comments

• When in doubt - Comment!!!• No effect on program execution

• Any text can be stored in a comment

• May take up part of a line, a whole line, more than one line

• Do not be stingy with Comments!!!

Examples of Comments

• Comments may use one line, part of a line, or more than one line:– /*A single line*/

– for (int x; x<10; x++) /*start of a loop*/

– /*Comments can span multiple lines– as well*/

Philosophy

• You never have too many comments• Too few comments may:

– cost you points in this class– cost you friends on the job– cause grey hairs

• Use comments when the logic is fresh in your mind

• Crucial to program maintenance