C BASICS

Content

C Lang Intro

Flow Control

Loops

Arrays

Example: Bubble sort

Example: Sieve of Eratosthenes

C Lang Intro

C Lang Intro

• Flexible & compact lang
• From operating systems to games
• Basis for more advanced langs
• Lang defined by an international standard (C11)
• Some elements in C11 optional
• C11 also defines a standard library for C
  • Common constants, symbols, functions, etc.
  • Optional extensions to C lang
• Machine-dependet facilities implemented in machine-independet   form (e.g. I/O)
• Standard library defined by a set of header files (.h)
• App dev includes the according headers

Compiler & Linker

• Compiler converts source code into machine lang

• Detects and reports errors

• Compiler outputs object code to object files (.obj, .o)

• Compilation phases

  • Preprocessing phase: source code may be modified or added

  • Actual compilation
• Linker
  • Combines object files
  • Adds required modules from std lib
  • Links everything to an executable
  • Also reports problems (reference errors)

C Development

1. Build with command line
   1. Start - Visual Studio Tools
   2. Developer Command Prompt - cd to dev folder
   3. cl main.c (compiles and links main.c)
2. Create C++ Project in Visual Studio
   1. File - New - Project
   2. Visual C++ - Empty Project
   3. Add a source file

First App

// main.c                        // This is a comment
#include <stdio.h>               // This is a preprocessor directive

int main()                       // Define function main
{                                // Mark beginning of main
    printf("Hi, there!\n");      // Print string to console
    return 0;                    // Return control to operating system
}                                // Mark end of main

Comments

// Comment 1: Compiler ignores everything with two slashes on a line

/* Comment 2 */

/* 
 * Comment 3:
 * Compiler ignores everything between /* ... */
 */

Preprocessing Directives

#include <stdio.h>         // # marks a preprocessing directive 

#define PI 3.1415          // define a constant

• Preprocessing directive tells the compiler to do something before comping
• Include header file into, define constants, etc...
• Header file provides info about types and functions in the stdlib
• Compiler uses info to integrate predefined functions or other objects to the app
• E.g. info about printf(..)

Functions

int main()     // Function header 
{              // Opening brace
    // ...     // Function body
}              // Closing brace

• Functions as named block of code that does something
• Every C app needs at least the main function
• Function signature
  • defines return type
  • defines function name
  • defines input parameters with types
• Keywords (reserved words) used to describe types (int, void, etc.)

Variables and Memory

• App and data is stored in RAM
• 0/1 in memory
• 8 bit groups - byte
• Each byte is labeled with a number (address)
• 1KB - 1024bytes
  • 1023 = 2^10 = 11 1111 1111
• Variables as piece of memory
  • with one or more contiguous bytes
  • 1, 2, 4 (32bit), 8, 16 bytes
  • every variable has a name
• Use variable name to store and retrieve data
• Variable type specifies data size

Variables #2

• Variable naming
  • May contain upper/lowercase letters
  • digits
  • underscore
• Must not begin with digit
• Different type of variables store different type of data

#include <stdio.h>

int main(void)
{
    int salary;         // Declare a variable called salary
    salary = 10000;     // Store 10000 in salary
    printf("My salary is %d.\n", salary);
    return 0;
}

Variables #3

• Variable declaration
  • introduces a variable name
• Variable definition
  • causes memory to be allocated
• Explicit/Implicit conversions
  • compiler performs implicit conversions when no data loss
  • explicit conversion needed if data loss possible

Flow Control

If Statement

if(a > b)
    printf('a is greater b');

if(a < b)
    printf('b is greater a');
else 
    printf('a is greater b');


if(a < b) 
{
    if(a < z) 
    {
        // ...
    }
    else 
    {
        // ...
    }
} 
else if(z < b) 
{
    // ...
}
else 
{
    // ...
}

Switch Statement

switch(customerId)
{
    case 35:
        printf('Customer id is 35');
        break;
    case 36:
        // ...
        break;
    default: 
        // ...
        break;
}

Loops

For Loop

for(int i = 0; i < 10; i++)
{
    // ...
}

int count = 0;
for( ; count < 10; ++count)
{
    // ...
}

for( ;; )
{
   // ...
   if(quitPrg)
        break;
}

• i is defined once
• loop expression is evaluated in each iteration
• variable i is incremented in each iteration

While Loop

int i = 0;
int count = 10;
while(i < count)
{
   //...
   i++;
}

for( ;; ) 
{
    // ...
    while(true)
    {
       // ...
    }
    // ...
}

Arrays

Arrays

#include <stdio.h>         // # marks a preprocessing directive 

• Preprocessing directive tells the compiler to do something before comping
•  Include header file into
• Header file provides info about types and functions in the stdlib
• Compiler uses info to integrate predefined functions or other objects to the app
• E.g. info about printf(..)

References

Beginning C (5th Edition)

Ivor Horton

Thank you for your attention!