C programming quick start

Content take from cprogramming.com

Intro

#include <stdio.h>

The #include is a "preprocessor" directive that tells the compiler to put code from the header called stdio.h into our program before actually creating the executable. stdio.h provides input output functions like printf & scanf.

int main() { }

Main body of program. Returns integer exit status to O.S. after execution. 0 = success, non zero is an error message.

hello world example

1. include <stdio.h>

int main() {

   printf( "Hello world!\n" );
   printf( "(hit enter to end)\n" );
   getchar();
   return 0;

}

compiling with gcc

gcc hello.c -o hello

run hello world and check exit status of last command

$ ./hello
Hello world!
(hit enter to end)

$ echo $?
0
$ ./hello
Hello world!
(hit enter to end)
^C
$ echo $?
130              <<<--- Script terminated by Control-C exit code

variables

types Char: a single character

Integer: number without decimal place

float: number with decimal place

placement

variable declarations must come before other types of statements in the given "code block"

comment syntax

/* comment text /*

conditional statements

and: & or: || not: !

examples

A. !( 1 || 0 )         ANSWER: 0	
B. !( 1 || 1 && 0 )    ANSWER: 0 (AND is evaluated before OR)
C. !( ( 1 || 0 ) && 0 )  ANSWER: 1 (Parenthesis are useful)

if, else if , else statement

if ( TRUE ) {
   /* Execute these statements if TRUE */
}
else if ( TRUE ) {
   /* Execute these statements if TRUE */
}
else {
   /* Execute these statements if FALSE */
}

loops

for ( variable initialization; condition; variable update ) {

Code to execute while the condition is true

}

example

   for ( x = 0; x < 10; x++ ) {
       printf( "%d\n", x );
   }

while ( condition ) { Code to execute while the condition is true }

example

 while ( x < 10 ) { 
     printf( "%d\n", x );
     x++;            
 }

do {

} while ( condition );

keywords

The break command will exit the most immediately surrounding loop regardless of what the conditions of the loop

break; 

The continue statement will stop the loop's current iteration, update itself, and begin to execute again from the top.

continue;

functions

prototype

return-type function_name ( arg_type arg1, ..., arg_type argN );

arg_type: int, float, char (examples)

the may be no arguments passed at all (where the parentheses are empty)

programmer defined function

int mult ( int x, int y );           /* function prototype goes in program "header" area above main /*
...
int main()
{
...
}

int mult (int x, int y)   /* function definition /*
{
  return x * y;
}

• note - no semicolon after argument section of function definition

case statements

switch ( <variable> ) {

case this-value:

Code to execute if <variable> == this-value

break;

case that-value:

Code to execute if <variable> == that-value

break;

...

default:

Code to execute if <variable> does not equal the value following any of the cases

break;

}

example

   printf( "1. Play game\n" );
   printf( "2. Load game\n" );
   printf( "3. Play multiplayer\n" );
   printf( "4. Exit\n" );
   printf( "Selection: " );
   scanf( "%d", &input );
   switch ( input ) {
       case 1:            /* Note the colon, not a semicolon */
           playgame();
           break;
       case 2:          
           loadgame();
           break;
       case 3:         
           playmultiplayer();
           break;
       case 4:        
           printf( "Thanks for playing!\n" );
           break;
       default:            
           printf( "Bad input, quitting!\n" );
           break;
   }