1. Variable Symbol represents a place to store information
name
value
memory space
Example: somebody’s age
An integer variable age;
age = 20;
Contrasted with constants
No change in constants
Computer memory
age 20

2. Why Need Variable Remember a value
Requests a value from the user
Results from calculation
Example:
int v1, v2, sum;
v1 = 50;
v2 = 30;
sum = v1 + v2;
* = means assign the value as
Provide a way to access your computer's memory
Computer memory v1 50 v2 30
sum 80

3. How – Declaration A variable must be declared before it can be used.
Tell the computer that you need to store a number in a variable
Mostly declared at the start of each function.
Declaration format:
type name = initial_value;
type name1 = initial_value1, name2 = initial_value2, …;
It is not required to put initial value in declaration

4. Declaration of Variables
type name = initial_value;
type name1 = initial_value1, name2 = initial_value2, …; {
int v1, v2, sum;
v1 = 50;
v2 = 30;
sum = v1 + v2; } {
int v1= 50, v2 = 30, sum;
sum = v1 + v2; }

5. Basic Types of Variables
int 
integer
float 
single-precision floating point
double
double-precision floating point
char 
one byte character
_Bool
Boolean

6. Variable Names Contain one or more characters,
A-Z, a-z
0-9 _
Must start with a non-digit character

7. Variable Names – cont. Cannot be C's keywords Limitation
int, main, while, etc
Limitation
Maximum of 63 characters for a variable name
Sometimes 31
or 8 in very old C
Case sensitive: upper and lower case characters are different
floating
int
Int
main3
4yi

8. int: integer Variables
For integral values only
10, -5, 1000
no fraction
10.2
no commas
12,000
Ranges
Machine dependent
Minimum: 16 digits
32 bits of storage on grove.ufl.edu (usual)
Signed: −2,147,483,648 to +2,147,483,647
Unsigned: 0 to +4,294,967,295
Maybe 64 on others

9. Operations for int type
Declaration
int x, y, z;
Assignment
y = 10;
z = 5;
Calculation
Plus: +
x = y + z;
Minus: -
x = y – z;
Muliply: *
x = y * z;
Divide: /
x = y / z;
Modulus
x = y % z;
result of y/z will be truncated

10. Display Integer Variables – I
Preprocessor: interact with input/output of your computer
#include <stdio.h>
int main()
Start point of the program { }
Start and finish of function
int value1, value2, sum;
Declear Variables
value1 = 50;
value2 = 30;
Define Values
sum = value1 + value2;
Summation
printf(“The sum of 50 and 30 is %i\n“, sum);
Print the value of an integer variable
Printing results
return 0;
Finish and return value 0

11. Display Integer Variables – II
#include <stdio.h>
int main() {
int value1, value2, sum;
value1 = 50;
value2 = 30;
sum = value1 + value2;
return 0; }
printf(“The sum of %i and %i is %i\n“, value1, value2, sum);

12. int: integer Variables – Special Case I
Starting with digit “0”
Octal notation. Base 8, not 10
0,1,2,3,4,5,6,7
0177 = 1*64 + 7*8 + 7 = 127
0256 = ?
Display
%i – print out the decimal value
%o – print out the octal value
%#o – print out the octal value, starting with 0

13. int: integer Variables – Special Case II
Starting with digit “0x”
Hexadecimal notation. Based 16, not 10
0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
0x177 = 1* * = 375
0xAF = ?
0x2AF = ?
Display
%i – print out the decimal value
%x – print out the hexadecimal value
%#x – print out the hexadecimal value, starting with 0

14. Example - I #include <stdio.h> int main() { int a, b, c, d;
d = 0xAF;
printf(“The four numbers are %i, %i, %#o, %#x\n”, a, b, c, d);
printf(“The four decimal numbers are %i, %i, %i, %i\n”, a, b, c, d); }

15. Example – II #include <stdio.h> int main() { int a, b, c, f;
f = a/b;
printf(“%i / %i = %i\n”, a, b, f);
f = b/a;
printf(“%i / %i = %i\n”, b, a, f);
f = c/a;
printf(“%i / %i = %i\n”, c, a, f); }

16. float: single-precision Variables
For values containing decimal
3., 125.8, -0.1
Scientific notation
2.25e-3 = 2.25 * 10-3 =
Use e or E for exponent
no commas

17. float Variables - II Ranges IEEE floating-point standard ±3.4×1038

18. float Variables - III Display %f – print out the decimal value
%e – print out the scientific notation
%g – let printf decide the format
-4 < value of exponent < 5: %f format
Otherwise: %e format

19. Operations for float type
Declaration
float x, y, z;
Assignment
y = 10.00;
z = 5.8;
Calculation
Plus: +
x = y + z;
Minus: -
x = y – z;
Muliply: *
x = y * z;
Divide: /
x = y / z;
result of y/z will NOT be truncated

20. Example – I #include <stdio.h> int main() { int a, b, c;
float f;
a = 10;
b = 20;
c = a/b;
printf(“%i / %i = %i\n”, a, b, c);
f = a/b;
printf(“%i / %i = %f\n”, a, b, f); }

21. double: double-precision Variables
Similar to float
More storage space (IEEE floating-point standard)
float variables: e+f+1 = 32
double variables: e+f+1 = 64
Ranges
± ×10308
Same display method as float
Operation similar as float

22. char: character Variables
For single character
Enclosing the character within a pair of ‘ ’
‘a’
‘;’
‘P’
‘\n’
‘1’
Display %c

23. Example – II #include <stdio.h> int main() { int a, b, f;
char c;
a = 36;
b = 52;
c = ‘a’;
printf(“The three numbers are %i , %i, %i\n”, a, b, c);
printf(“The three characters are %c , %c, %c\n”, a, b, c); }

24. _Bool: Boolean Type For boolean Display 0/1 Normally means false/true

25. Finish the Code #include <stdio.h> int main(void) {
int integerVar = 100;
float floatingVar = ;
double doubleVar = 8.44e+11;
char charVar = ‘W’;
_Bool boolVar = 0;
printf(“integerVar = %? \n”, integerVar);
printf(“floatingVar = %? \n”, floatingVar );
printf(“doubleVar = %? \n”, doubleVar );
printf(“doubleVar = %? \n”, doubleVar ); // scientific notation
printf(“charVar = %? \n”, charVar );
printf(“boolVar = %? \n”, boolVar );
return 0; }

26. Special variable types
short
usually use less space
add “h” after “%” in printf
long, long long
usually use more space
use “l” to indicate
add “l” after “%” in printf
signed, unsigned
specify whether is a signed quantity
use “u” to indicate unsigned
%u for unsigned

27. Summary of Data Type Type Examples Printf char ‘a’, ‘\n’ %c _Bool 0, 1
%i, %u
short int
1,100, -5
%hi, %hx, %ho
unsigned short int
1, 39, 100
%hu, %hx, %ho
int
-1, 5, 0XAF, 0177
%i, %x, %o
unsigned int
5u, 0XAFu, 0177U
%u, %x, %o
long int
0xffffL, 12l
%li, %lx, %lo
unsigned long int
0xffffUL, 12ul
%lu, %lx, %lo

28. Summary of Data Type – cont.
Examples
Printf
long long int
0xffffLL, 12ll
%lli, %llx, %llo
unsigned long long int
0xffffULL, 12ull
%llu, %llx, %llo
float
12.3f, 3.1e-5f, 0x1.5p10
%f, %e, %g %a
double
12.3, 3.1e-5, 0x1.5p10
long double
12.3l, 3.1e-5l
%Lf, %Le, %Lg

29. Assignment Operators Join the arithmetic operators Examples:
Format: op=
Examples:
count = count + 10;
count += 10;
count = count - 5;
count -= 5;
a /= b + c;
a = a / (b + c);

30. Unary Operators M += 1; M = M + 1; ++M; M++; Unary plus / minus
+ / -
Example: -a
Unary increment/decrement
++ / --
M += 1;
M = M + 1;
++M;
M++;

31. Arithmetic Operators
add: +, minus: -, multiply: *, divide: /, modulus: %
Parentheses (grouping): ( )
Unary plus / minus + -
Unary increment/decrement ++ --

32. Operator Precedence Precedence Order for
Operators with higher precedence are evaluated first
Operators with same precedence are evaluated from left to right
In decreasing precedence
( )
unary increment (++), unary decrement (--)
unary plus (+), unary minus (-)
multiply (*), divide(/), modulus(%)
add(+), minus(-)
Order for
c = -a * b
a + b * c / d