Further C Programming

1

• Further C Programming
• Variable types
• Loops
• Conditional statements
• Local and Global variables
• Arrays
• Pointers

2
Types

• Variable Types
• char character
• short short integer -32767 to 32767
• int integer -/2,147,483,647
• long int long integer -/
  9E18
• float floating point 1.2E-38 to 3.4E38
• double double precision 2.2E-308 to 1.8E308

3
for loop

• Can set up loops to repeat sections of code
• for (count 1 count lt3 count)
• printf("d \n", count)

• count is short hand for countcount1

4

• While Loop
• Useful when we dont know how many times the loop
  will repeat.
• Eg
• while (agt0)
• fscanf(fin,"d d",a,b)
• c ab
• printf("d d d \n", a,b,c)
• Use to read a file to the end.
• while(!feof(fin))fscanf(fin,d d,a,b)

5

• Conditional Statements
• Most common example is the ifelse construction
• Eg
• if(mark gt 40)
• printf(pass\n)
• else
• printf(fail\n)
• Boolian operators
• 
  !
• Equals And Or
  Not

6

• Functions and Variables
• Common mathematical functions are defined in the
  header file math.h
• include ltmath.hgt
• Often useful to define your own functions.
• Functions must be prototyped before the main()
  loop is reached.

7
/ Program to calculate the product of two
numbers / / and the sine of the product/
include ltstdio.hgt include ltmath.hgt int
product(int, int) int main(void) int
a,b,c printf ("Enter a number between 1 and
100 ") scanf ("d", a) printf
("Enter a number between 1 and 100 ") scanf
("d", b) c product(a,b)
printf("d times d d \n", a, b, c)
printf("sin(d times d) f\n",a,b,sin(c))
return(0) int product(int x, int
y) int z zxy return(z)
8

• Variables declared within a function are local to
  that function.
• i.e. their values are only know within the
  function.
• Changes made to the variables are not known
  outside the function.
• Variables declared above the main() loop are
  global variables.
• i.e. their values are known anywhere in
  the program.
• Changes can be made anywhere in the program.

9
/ Program to calculate the product of two
numbers / / and the sine of the product/
include ltstdio.hgt include ltmath.hgt int
product(void) int a,b int main(void)
int c printf ("Enter a number between 1 and
100 ") scanf ("d", a) printf
("Enter a number between 1 and 100 ") scanf
("d", b) c product()
printf("d times d d \n", a, b, c)
printf("sin(d times d) f\n",a,b,sin(c))
return(0) int product(void) int
z zab return(z)
10

• Arrays
• If you have lots of variables of the same type it
  is inconvenient to have to define each separately
• Eg. data1, data2, data3,
• Arrays are a way of storing a set of like
  variables
• Eg. double data100
• Values can be assigned directly
• Eg. double x423.4, 54.6, 66.1, 76.2
• or using loops
• Eg. for(i0 ilt4i)
• xisin(iM_PI/4)

11

• For an array xN of size N, the elements are
  labelled
• x0, x1, x2, xN-2, xN-1
• Can be used just as other variables
• Eg.
• Sum20
• for(i0iltNi)
• sum2sum2xixi
• A common mistake is to access array elements that
  dont exist.
• Eg. xN

12
Multidimensional Arrays

• int random_array101010
• for(a0alt10a)
• for(b0blt10b)
• for(c0clt10c)
• random_arrayabcrand()

13

• Pointers
• When we define a variable x, the computer labels
  a part of the memory x and stores the value of x
  in that part of memory.
• We can then use x as a variable in our
  calculations.
• Another way of accessing the variable x would be
  to know where it is stored, i.e. its address.
• We can define a pointer to x as a new type of
  variable that stores the address of the variable
  x.

14
include ltstdio.hgt int main(void) double x
double p px x2.0
printf(xf\n, x) p3.0
printf(xf\n, x) return(0)
15

• Pointers can be passed to functions to allow them
  to change more than one variable.
• Eg.
• include ltstdio.hgt
• void increase(int , int , int )
• int main(void)
• int x,y,z
• increase(x, y, z).
• void increase(int px, int py, int pz)
• pxpx1
• pypy1

16

• Pointers and arrays are closely related.
• x0, x1, x2. are variables (eg.
  doubles).
• x0, x1, x2are their addresses.
  
• BUT
• x is a pointer to x0.
• Arrays elements can be accessed in two ways
• xi is the same as (xi)

17

• Arrays can be passed between functions simply by
  passing a pointer to the first array element.
• Much quicker than copying one array to another.
• If you change elements of the array within the
  function, these changes will be known everywhere
  in the code.

18
include ltstdio.hgt define N 5 void mean(double
) int main(void) int i double xN
for(i0iltNi) printf(input value d
,i) scanf(f,xi) mean(x)
return(0)
void mean(double x) int i double sum
sum0.0 for(i0iltNi) sumsumxi
printf(Mean f\n,sum/(N))