C Programming Flashcards

Introduction to C

Introduction

• C is a general-purpose programming language.
• Developed by Dennis Ritchie at Bell Labs during the development of Unix in 1972-73.
• The Unix system and most programs that run on Unix are written in C.
• C is called a “System Programming Language” because it's useful for writing compilers and Operating Systems.
• C has been equally used in writing applications/software in other domains.

C as a Low-Level Language

• C is relatively a low level language.
• Designed such that its constructs can efficiently map with machine instructions (machine code).
• Therefore, C easily interacts with hardware, e.g., RAM, CPU.
• Devices formerly coded using Assembly Language now use C, from supercomputers to embedded systems.

C as a Cross-Platform Language

• C is a cross-platform language.
• A program written on one machine can be executed on another machine.
• You don’t have to rewrite the program for another machine, unlike Assembly or Machine Language.

First C Program

• A C Program consists of functions and variables.
• A program may contain several functions.
• In every C Program, there is a special function main().
• Your program begins executing at the beginning of main.
• Within the main function, you may call other functions.
• The first line of the program is #include <stdio.h>.
• This line tells the compiler to include information about the standard input/output library.
• This line appears at the beginning of many C source files/programs.

Elements of a C Program

• A C development environment includes:
  • System libraries and headers: a set of standard libraries and their header files (e.g., /usr/include and glibc).
  • Application Source: application source and header files.
  • Compiler: converts source to object code for a specific platform.
  • Linker: resolves external references and produces the executable module.
• User program structure:
  • There must be one main function where execution begins when the program is run. This function is called main.
    • int main (void) { ... }
    • int main (int argc, char *argv[]) { ... }
    • UNIX Systems have a 3rd way to define main(), though it is not POSIX.1 compliant int main (int argc, char *argv[], char *envp[])
  • Additional local and external functions and variables.

C Standard Header Files

Standard Headers you should know about:

• stdio.h – file and console (also a file) IO: perror, printf, open, close, read, write, scanf, etc.
• stdlib.h - common utility functions: malloc, calloc, strtol, atoi, etc.
• string.h - string and byte manipulation: strlen, strcpy, strcat, memcpy, memset, etc.
• ctype.h – character types: isalnum, isprint, isupper, tolower, etc.
• errno.h – defines errno used for reporting system errors.
• math.h – math functions: ceil, exp, floor, sqrt, etc.
• signal.h – signal handling facility: raise, signal, etc.
• stdint.h – standard integer: intN_t, uintN_t, etc.
• time.h – time-related facility: asctime, clock, time_t, etc.

Writing a C Program

• Open Terminal on Seed Virtual Machine.
• Create a folder in your home directory (/home/seed).
  • mkdir Cprograms
  • cd Cprograms
• Open a text editor using the following command:
  • sudo gedit helloworld.c
• Using the above command, you are opening a text editor and naming the file as helloworld.c (.c is an extension for all C files).
• Type the program you just learned in the text editor.
• Once you have finished writing it, go to the file tab and click save.
• Save this file in the Cprograms folder.

Running a C Program

• To run a C Program, you first need to compile the program.
• If you are not in the Cprograms directory, in the terminal, browse to that directory.
• To compile, use the following command:
  • gcc –o helloworld helloworld.c
• After the file is compiled, if you list the contents of this folder, you will notice a new file just created with the helloworld name (this is an executable file).
• In the terminal, now type the following to run the program:
  • ./helloworld

Variables and Arithmetic Expressions

• Write a program in C that converts Fahrenheit into centigrade or Celsius equivalents:
  • Formula: C = (5/9)(F-32)

Variables

• A variable is a named space in memory to store data.
• In C, all variables must be declared before they are used, usually at the beginning of the function before any executable statements.
• A declaration tells the properties of variables.
• It consists of a type name and a list of variables.
  • Example:
    • int fahr, celsius;
    • int lower, upper, step;
• The type int means that the variables listed are integers.
• Another data type is float - numbers that may have a fractional part.
• The range of both int and float depends on the machine you are using.
  • A 16-bit integer will hold values between -32768 and +32767.
  • A 32-bit integer will hold values between -2,147,483,648 to 2,147,483,647.
• C provides several other basic data types besides int and float, including char, double, etc.
• After being declared, a variable is usually initialized to some initial value before being used.
• A variable has a type and a name.
  • int int1; // declares an integer named int1
  • double d; // declares a double
  • int1 = 5; // int1 is given the value 5
  • int int2 = 3; // int2 is declared and initialized

Variable Declaration Syntax

• Example:
  • float x;
  • double d = 5;
  • int *p, i, a[100];
  • char s[21];
• Syntax: type variable_name, ... [= value];

Changing Variable Values

• Example 1:
  • int x, y, z;
  • x = 2;
  • x = x + 1;
  • y = z = 4 + 5;
  • x += 1;
  • ++x; //Pre increment
  • x++; //Post increment
  • y = x--;
• Example 2:
  • int i, j;
  • i = 1;
  • j = 1;
  • j = i++;
  • `printf (“Value of j is %d\n Value of i is %d\n