C Programming Flashcards

Introduction to C

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 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 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.

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.

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.

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.

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.

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

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

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