IT REVIEWER – C
Below C Level
Origin
- Developed at AT&T Bell Labs in early 1970’s
- Created by Dennis Richie
- Product of both the B Programming Language and BCPL
Characteristics
- Programming languages have different levels, depending on how they resemble human
languages
1. Low-level Languages
2. Mid-level Languages
3. High-level Languages
Low-level Languages High-level Languages
-consists of numbers and codes that the -reads almost like English; all its commands &
microprocessor understands and executes instructions are English words
EX: Assembly Language EX: BCPL
ADVANTAGES:
High-level Low-level
M
I
D
- - runs programs faster
- easier to implement L - produces smaller program
E size
V
E
L
Mid-level Language
-compact program size
-easy development
-fast running time
EX: C
Editing, Compiling, and Running a C Program
(syntax – structure, sematics – meaning) *
GCC – GNU Compiler Collection
Compiler
- examines each
- reads the instruction instruction - translates the
from the code information
(tells errors)
computer - links the object code - GCC creates object
program file code file
Development Cycle
1. Save!
2. Compile and Link!
3. Run!
4. Do it Again!
1. Save – saving the source code
- Create a source code in a text editor
- Save it as a C file using .c as extension
2. Compile and Link
- Source code to object file
- Object file to executable file
3. Run
- Program runs on a terminal
EX:
1. Save world.c
Filename: world
File extension: .c
2. Compile and Link gcc -o hello world.c
Compiler: gcc
Linker: -o (object file - determines name of executable file)
Executable File: hello
File: world.c
3. Run ./hello (runnable in terminal)
Executable file: hello
Common Errors
1. Wrong file extension
2. Using a forward slash (\) when a blackslash (/) is required
3. Forget to put on & on arguments, causes SEGMENTATION FAULT
SEGMENTATION FAULT – lacking argument, parameter, or variable
4. Missing closing and terminating characters, causes SYNTAX ERROR
- omitting a semicolon (signifies end of line) or a closing brace
- omitting quotation character
Basic Parts of a C Program
#include <stdio.h>
intmain (){
printf (“hello world!\n”);
return 0;
}
#include – directory
- instructs the compiler to include another source file
<stdio.h> or “stdio.h” – header file (.h)
- Provide protoype declarations for library functions
Libraries:
<stdio.h>
- standard input output
<math.h>
- math operations
<stdlib.h>
- standard library
<string.h>
- string manipulation
intmain(){
} - main function
- Curly brackets close body
- Performs the principal function of a program
printf (“hello world!\n”);
return 0; - main body (in between curly braces)
return 0; - terminates program
\n – new line
Variable Declaration
Variables
- Temporary holders of values with a specified data type.
Data Type
- size and range of values and operations
- Do not use numbers as a first character
- No spaces (use underscore)
- C is case sensitive!
EX: number1 V 1number X number 1 X number_1 V
Data Types in C
Data Type Name Format Specifier Description
void Void Absence of type
int Integer %d or %i Whole numbers
char Character %c Letters on symbols
float Float %f Floating point numbers
(six decimal places)
double Double %lf Floating point numbers
(fifteen decimal places)
Reserved Words
- Cannot be declared as variables; cannot be used as variable names.
EX: return
Comments
// - ignores a line
/* */ - used for multi-line comments
EX:
/*
This is a function in C
*/
//comment
Input and Output Statement
Printing a Statement
In Pseudocode In C
DISPLAY “hello world” printf(“hello world”);
Getting an Input
scanf (“%d”, &number);
Built in function: scanf ()
Formal specifier: %d
Variable name: number
& - locates variable in a computer
EX:
printf(“There are %d students in this class.”, number);
