Programming - Functions & scope of variables(5)

Administrivia

Practice Web Page - http://www.cs.tau.ac.il/~efif/courses/Programming_Fall_04

switch, do, while, and for

The switch statement
- similar to the if-else if-else "statement"
- allows the selection of an arbitrary number of choices based on an integer value
  switch (expression) {
    case const-expr: statements
    case const-expr: statements
    …
    default: statements
  }

Calculate

using 3 methods

/* Calculate Pi according to various methods */
#include <stdio.h>
#include <math.h>
int main()
{
  <scan option>
  switch(opt) {
   case 1:
    <scan num>
    pi = pi1(num);
    break;
   case 2:
    <scan epsilon>
    pi = pi2(epsilon);
    break;
   case 3:
    <scan epsilon>
    pi = pi3(epsilon);
    break;
   defualt:
    <issue error message>
    break;
  }
  <print pi>
  return 0;
}

is_prime.c

Functions on characters

A function that checks for an alphabetic character

int is_alpha(char ch)
{
  return (('a'<=ch && ch<='z')||('A'<=ch && ch<='Z'));
}

A function that checks for a digit (0 through 9).

int is_digit(char ch)
{
  return ('0' <= ch && ch <= '9');
}

count.c

Another example

Calculate e according to:

/* Calculate e according to (1 + 1/n)^n */
#include <stdio.h>
double calc_e(int alst);
int main()
{
  int last;
  printf("Enter number of iterations: ");
  scanf("%d", &last);
  printf("%lf\n", calc_e(last));
  return 0;
}
double calc_e(int last)
{
  int i;
  double e = 1, mul = 1 + 1 / (double)last;
  for (i = 1; i <= last; i++)
    e *= mul;
  return e;
}

Another example

The root of a number a can be calculated according to:

/* Calculate the root of a number */
#include <stdio.h>
double my_sqrt(double num)
{
  double root, root_n = 1.0;
  do {
    root = root_n;
    root_n = (root + num / root) / 2;
  } while(root_n != root);
  return root;
}
int main()
{
  double num;
  scanf("%lf", &num);
  printf("%lf\n", my_sqrt(num));
  return 0;
}

my_sqrt.c

Variable scope

scope - the region of the program code in which declaration has effect
- local variables: declaration through to end of block
  - parameters: through to end of function
- global variables: declaration through to end of file

A program that counts the number of times it is invoked

#include <stdio.h>
int invoke()
{
  static int counter = 0;
  return ++counter;
}
int main()
{
  int i;
  for (i = 0; i < 10; i++)
    (void) invoke();
  printf("%d\n", invoke());
  return 0;
}

invoke.c

Maintained by Efi Fogel. Last modified: December 08 2003.