Intro to Programming in C
Motivation for Using C
 High
level, compiler language
 Efficiency
 Allows
over user-friendliness
programmer greater freedom, but
chance for is error increased
Functions

C includes support for functions

Function structure
return_type function_name(parameters)
{
variable declarations;
body statements;
return return_value;
}

Example:
int add_function(int a, int b) /* Pass values a and b to function */
{
int sum;
sum = a + b;
return sum; /* Returns the integer variable sum */
}
Main Function
 Each
C program contains a main routine, which
is itself a function
 The
main routine typically returns no value and
contains no parameters, so the default return
type is “void”
 Example:
void main(void)
{
main routine
}
Creating Functions


Convention is to place function “prototype” above the
main routine
Prototype includes function name and variables used:
int add_function(int, int); /* function prototype */
main routine
…

Function body defined below main routine:
main routine
{…}
int add_function(int a, int b);
{ function body};
Calling Functions
 Call
a function by invoking its function name
within the main routine or another function and
passing parameters
 Example:
void main(void)
{
int a,b,x;
…
x = add_function(a, b); /* Passed by value */
}
/* x is set equal to the return value of add_function */
Basic Data Types

Int
• Represents standard integers (usually 32 bits)

Float
• Represents numbers with decimal precision (usually 32 bits)
• Can use notation: 2.3E10  2.3 * 10^10

Double
• Represents very large floating point numbers
(usually 64 bits)

Character (Can also declare “byte” when using Processor Expert)
• Represents single ASCII characters
• Characters contained within single quotes: ‘a’

No String types!
Data Type Modifiers

Signed
• Allows the data type to take on negative and positive values
• Integers, doubles, and floats are signed by default

Unsigned
• Allows the data type to take on only positive values

Short
• Reduces range of values and storage space occupied by the
variable (usually 16 bits)

Long
• Increases range of values and storage space occupied by the
variable (usually 32 bits)
Declaring Variables

Variables are defined using the following format:
type name1, … , name5;

Name rules:
•
•
•
•
•

Cannot begin with a number
Cannot contain spaces (can contain underscores)
Cannot contain any punctuation marks or arithmetic operators
Cannot be a reserved keyword
C is case sensitive!
Examples
int a, b, c;
short int d;
unsigned double e;
float f;
char g;
…
Initializing Variables
 Possible
to initialize variables within
declaration:
int a = 3;
byte x = 0x02; byte y = 0b00000010;
char b = ‘b’;
 Constants
• Use keyword “const”
• Constants cannot be changed after initialization
• Example:
const int b = 5;
Assigning Variables
 Valid
assignments
int a,b; int c = 5;
a = 10;
a = c;
a = b = c = 0;
 Type
Casting
• Possible to convert between several types:
(type) variable_name
• Examples:
x = (int) float_variable /* Converts a float to an integer
x = (int) char_variable /* Converts a character to ASCII value
x = (char) int_variable /* Converts ASCII to appropriate character
x = (float) int_variable /* Converts an integer to a float
Variable Scope
 Global variables
• Declared above the main routine, normal syntax
(convention is to use all caps)
• Available to all functions
• Global constants declared using:
#define VARIABLE_NAME value
 Local variables
• Declared within a function
• Only available to the function in which declared, able to
pass on to other functions
Pointers



Used to point to a memory location of a variable
Points to the beginning of the memory segment the
variable occupies
Use the ‘*’ operator in front of variable to declare a
pointer
float test_var;
float *test_var_loc;

Use the ‘&’ operator to get the memory location of non-pointer
variables
test_var_loc = &(test_var)
Pointer Operations
 Using
the ‘*’ in front of an already declared
pointer yields contents of memory location
pointed to
 Example:
int test_var = 10;
int X;
int *location;
location = &(test_var);
X = *location;
/* The variable X now contains the value 10
Pointer Operations (cont.)
 Possible
to assign values to memory
location using pointer
 Example:
int test_var = 10;
int *location;
location = &(test_var);
*location = 20;
/* The variable test_var now contains the value 20
Function Calls Using Pointers
 Possible
to pass “by reference” using pointers
 Example:
void set_zero( int *a)
{
*a = 0;
}
void main()
{
int b = 10;
set_zero(&b);
/* b is now set to zero */
}
Pointer Notes
 Not
useful to initialize pointers in the
declaration:
• Initially, pointer points to “garbage” location, so
assigning a value to this location is useless
 Useful
in debugging
 Used
heavily in string manipulation
 Make
linked-lists possible
Arrays
 Arrays
are defined as follows:
type var_name[size]

Array index begins at zero

Array index ends at size – 1

Example:
int array1[3] = {1, 2, 3}
/* array1[0] = 1, array1[1] = 2, array1[2] = 3 */
Arrays (cont.)
 Multidimensional
arrays:
int multi_array[10][10]; /* 10x10 array */
 Possible
to use as many dimensions as
needed
 Can
initialize entire array at once:
multi_array[ ][ ] = 0;
Strings
 There
is no “string” type in C
 Strings
made possible through character
arrays
 Declared
as a pointer to a character or an
array of characters
Creating Strings
 Pointer method
• Creates a pointer to the first location of the
string
char *test_string = “Hello World”;
• Strings always terminated with the null
character: ‘\0’
 Array method
• Easier to understand
char test_string[20] = “Hello World”;
String Manipulation

Many useful functions contained within “string.h”
• strlen(string) returns the length of the string excluding the null
character
• strcpy(string1, string2) copies contents of string2 into string 1
• strcmp(string1, string2) compares string 1 to string 2, returns 1
if same and 0 if different
• strstr(string1, string2) searches string1 for the substring string2,
returns the location at which the substring begins or null
• strcat(string1, string2) concatenates string2 onto the end of
string1
Structures

Creates a new data type that can hold several data types within
one variable

Use “struct” keyword
typedef struct
{
char name[30];
char address[50];
int birth_year;
int birth_month;
int birth_day;
} PersonalData;

Declare variable of type PersonalData
PersonalData record1;

Access struct using dot notation
record1.name = “Sam Castillo”;
Arithmetic Operations
 Addition: +
• a + b  Adds a to b
 Subtraction: • a – b  Subtracts b from a
 Multiplication: *
• a * b  Multiplies a by b
 Division: \
• a \ b  Does integer division of a by b
 Modulus: %
• a % b  Returns remainder of a \ b
Comparison Operators
 Greater
than: >, >=
• a >= b  Tests if a is greater than or equal to b
 Less
than: <, <=
• a <= b  Tests if a is less than or equal to b
 Equal
to: ==
• a == b  Tests if a is equal to b
 Not
equal: !=
• a != b  Tests if a is not equal to b
Bit Operators
 Shift Left: <<
• a << b  Shifts bits in a left by b bits
 Shift Right: >>
• a >> b  Shifts bits in a right by b bits
 And: &
• a & b  Does the bit-wise AND of a and b
 Or: |
• a | b  Does the bit-wise OR of a and b
 Exclusive OR: ^
• a ^ b  Does the bit-wise XOR of a and b
Other Operators

One’s compliment: ~
• ~a  Performs one’s compliment of a

Pre-increment: ++
• ++a  the value of a after incrementing

Post-increment: ++
• a++  the value of a before incrementing

Pre-decrement: -• --a  the value of a after decrementing

Post-decrement: -• a--  the value of a before decrementing

Negation: !
• !a  does the negation of a
If statements
 Basic
structure:
if (test_statement)
{
do this if test statement is true;
}
else if (test_statement)
{
do this if test statement is true;
}
else
{
do this if the above conditions were false;
}
Alternative If Statement


C provides a more concise way to create an If
statement
The syntax:
decision statement ? true statement:false statement

Example
int X = 4;
X == 5 ? X = 6 : X = 7;
/* First, the program checks if X is equal to 5
If X was equal to 5, then X would be set equal to 6
Since X wasn’t equal to 5, X is set to equal 7 */
For Loops

Basic structure
for(control variable; loop condition; increment)
{ statements; }

Example:
int count;
int a = 1;
for(count = 1; count <= 5; count++)
{
a = a*2;
}
/* Here a = 32 when the loop completes */

Cannot declare control variable within the for loop!

Can exit a for loop at any time with the statement “break”
While Loops
 While loop:
• Condition is evaluated each time the loop runs, including
the first time it is called
while(condition)
{statements; }
 Do While loop:
• Statements are executed the first time, then execution
depends on whether the condition evaluates to 1
do { statements; }
while(condition)
Printing to the Screen
 Output
to the screen using “printf”
function
 Structure:
printf(“Text…”, variables used);
 To
insert variables, must use “control
sequences”
Printf Control Sequences
 Denoted
with a “%”
• %d  integers, doubles
• %u  unsigned integers
• %c  characters
• %s  strings (character arrays)
• %f  fixed floating point values
• %e  scientific notation floating point
• %x  hexadecimal values
• %o  octal values
Inserting Control Sequences
 Insert
the sequences in the Text portion
of the printf statement
int a = 20;
char c = ‘b’;
printf(“The value of a is %d.”, a);
printf(“The value of c is %c.”, c);
Output Formatting

Padding the end of the output
printf(“%6d, int_val) /* Pads up to 6 places

Padding the start of the output
printf(“%-6d, int_val) /* Pads up to 6 places

Floating point precision
printf(“%.3d, float_val) /* Prints 3 decimal places

Truncating strings
printf(“%.3s, string_val) /* Prints first 3 characters

Truncating and Padding
printf(%10.5, string_val) /* Prints first 5 characters, pads last 5
Outputting Special Characters
 Possible to output with
• \b  backspace
• \f  form feed
• \n  new line
• \r  carriage return
• \t  horizontal tab
• \v  vertical tab
• \”  double quote
• \’  single quote
• \\  backslash
• \ddd  octal ASCII code
• \xddd  hex ASCII code
the following codes:
Receiving Keyboard Input
 Using
the “scanf” function
scanf(“String…”, pointers);
 Must
use control sequence, different from printf
 Must
use “&” when referring to input variables
 Example:
scanf(“%d”, &int_var);
scanf(“%f”, &float_var);
scanf(“%c”, &char_var);
Scanf Control Sequences
 Denoted
with a “%”
• %d  integers
• %ld  long integers
• %h  short integers
• %c  single character
• %s  strings (character arrays)
• %f  fixed floating point values
• %lf  long float type
• %e  scientific notation floating point
• %x  hexadecimal values
• %o  octal values
Dangers of Scanf
 Scanf
can cause many errors if used
incorrectly
 The
control sequence used must match
the type of variable that is storing the
input
 If types don’t match, scanf quits
• Input file will hold onto data, which is used in
next scanf call
Including Separate Files

Start by including all necessary libraries and files
before the main routine

Use the #include operator to include each header-file
as needed

Example:
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

Include all function headers before the main routine
Commonly Used Libraries
 Stdlib.h
• Contains many of C’s general use functions
 Stdio.h
• Contains all input/output functions
 Math.h
• Contains many math-related functions
 String.h
• Cointains all string manipulation functions
Creating Header Files
 Create
desired functions within a text
editor
 Save
with the .h extension
 Include
the header file within the main
program using the #include< > operator
Header File Example
 Header
File: test.h
 Main
int testfunction1( )
{
function body…
}
int testfunction2()
{
function body
}
…
file
#include<test.h>
…

Now have access to all
functions defined within
test.h
Putting it all together

Example Program Structure
#include …
#define …
Global variable declarations…
function prototypes….
main routine
{
local variable declarations
main body
function calls
}
function definitions…
{
local variable declarations
body statements
return
}