Computer Langueges

Controlling hardware

• (e.g., Chipset, Microcontroller, etc.)
  
• hardware needs software to function
• hardware prefers low level languages (due to Mem and CPU consumption)
• Sol: C

C is a foundational programming language

Why C?

• General-purpose (oringially designed for UNIX) (wide range of application)
• Provides common ancestry (c#,c++, etc.)
• Structured programming language (Funcation, loops, etc.) readable
• Machine-independent (i.e., can be executed on different architectures without significant modifications)
• Low level (small degree of abstraction from the hardware, and direct manipulation)

c advantages

First Program in C

This is the first program we are going to create in C.

// library or header file that contains  standard input/output operatioins

#include <stdio.h>   

/* 
  main() function every C program must have a main, 
  it has a returnable 'int' this is for exit codes
*/
int main(void) // void means no input argument
{
    printf("Hello World!\n");
    printf("Goodbye World!\n");
    return 0; // return exit code 0, no error
}

Compile the code

We are going to use gcc compiler to compile our c code; first argument is the source file[s], and -o means output file. The file extension in linux can be left blank or called whatever you want.

$ gcc helloworld.c -o helloworld.[out,exe,...]

Execute the code

As we are using a terminal, we must prepend the newley created file with ./. The . denotes the current directory. Since we want to run a file in our current directory and that directory is not in our $PATH, you need the ./ bit to tell the shell where the executable is.

Output:

$ ./helloworld.exe
Hello World!
Goodbye World!

Header Files

Libraries

These files contain all scaffolding code that your main() will use as we do not want to overpopulate with excessive lines of code for readability.

Computers used to be too slow to compile a whole program in one single mega-blob where all the functions and types were visible.

To solve this, programs are split into c/h files which are each individually compiled into a machine code file (the ‘object’ file), and then linked together into an exe or dll.

Header Files Continued

usefulfunctions.h

#ifndef USEFULFUNCTIONS_H_   /* Include guard */
#define USEFULFUNCTIONS_H_

int sqr(int x);  /* An example function declaration */

#endif // USEFULFUNCTIONS_H_

usefulfunctions.c

#include "usefulfunctions.h"  /* Include the header (not strictly necessary here) */

int sqr(int x)    /* Function definition */
{
    return x * x;
}

Revist helloworld.c

We are modifiying the code to use our custom library:

#include <stdio.h> /* searches system header file directories */
#include "usefulfunctions.h" /* notice "" searches current directory */

int main(void) /* void means no input argument */
{
    printf("Hello World\n!");  /* using standard ouput function to printf()*/
    printf("%d\n",sqr(255));
    printf("Goodbye World!\n");

    return 0; /* return exit code 0, no error */
}

Compile and run again

We need to source all files needed to build our modified program.

Remember the header file points to the function in the usefulfunctions.c file.

$ gcc helloworld.c usefulfunctions.c -o helloworld.out

Output:

$ ./helloworld.out
Hello World!
65025
Goodbye World!

Standard Input and Output

• stdio.h is a large file that contains many function declarations, in fact there are 827 lines of code for this header file alone.

  • stdio.h source code

You should feel a sense of accomplishment for the code you have written so far... just remember that someone wrote the code for your code to work .

Primitive Data Types

C has several data types and all variables must have a data type.

C Advanced Features

• Pointers and addressing, int*, &var1 (more about this later)
• struct
  • Allows to combine data items of different kinds
  • struct Books { char title[50]; char author[50]; int book_id;} book
• enum
  • It consists of constant integrals or integers that are given names by a user.
  • enum enum_name{int_const1, int_const2, int_const3, …. int_constN};
• union
  • allows to store different data types in the same memory location
  • union Data { int i; float f; char str[20];} data;

Embedded C

ANSEL  = 0;      // Configure AN pins as digital I/O
ANSELH = 0;
C1ON_bit = 0;    // Disable comparators
C2ON_bit = 0;
//         76543210
TRISC  = 0b10000000;   // PORTC is input
UART1_Init(9600); // Initialize UART PROTO

...

ANSELA  = 0;      // Configure AN pins as digital I/O
ANSELB  = 0;
ANSELC  = 0;
TRISB = 0;

Objective-C

#import "MyClass.h"
 
@implementation MyClass
- (id)initWithString:(NSString *)aName
{
    // code goes here
}
 
+ (MyClass *)myClassWithString:(NSString *)aName
{
    // code goes here
}
@end

Compilation

Command Line Arguments

#include <stdio.h>

int main( int argc, char *argv[] )  {

   printf("Program name %s\n", argv[0]);
 
   if( argc == 2 ) {
      printf("The argument supplied is %s\n", argv[1]);
   }
   else if( argc > 2 ) {
      printf("Too many arguments supplied.\n");
   }
   else {
      printf("One argument expected.\n");
   }
}

Lab:Let's do this now...

• Link to the lab