Difference between revisions of "C programming quick start"

Revision as of 21:14, 10 July 2014

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;