ECE 10 Dr. Klefstad Iteration and Simple Arrays

Outline

Iteration Statements
- for
- while
- do while
Simple Arrays
Character Strings

The Concept of Iteration

also called `looping'
allows repeating a similar action several times
the break statement will exit any loop
the return statement will also exit the loop

The for Statement

the most common loop statement
Natural for initializing, testing, then advancing

abstract examples

for ( each student, s, in this class )
  assignGradeTo( s );
for ( each day, d, of the quarter )
  studyHardOnDay( d );
for (each station, s, on the radio tuner )
{
  tuneRadioTo( s );
  if ( youLikeTheSong( listen() )
    break; /// terminates this for loop
}
for ( each integer, i, in the range 0 to 9 )
  cout << i << endl;

real examples

// print out numbers 0 through 9
for ( int i = 0; i < 10; i++ )
  cout << i << endl;
// read 10 integers from the input and print the sum
int main()
{
  int valueRead = 0;
  int sumTotal = 0;
  for ( int i = 0; i < 10; i++ )
  {
    cin >> valueRead;
    sumTotal += valueRead;
  }
  cout << "The total is: " << sumTotal << endl;
}

The while Statement

Natural for testing BEFORE doing an action that involves repetition

while ( isTooSour(coolade) )
  addATeaspoonOfSugar(coolade);
while ( isTooCold(bathtub) )
  addGallonsOfHotWater(bathtub, 1);
while ( ! understandTheHomeworkAssignment(student) )
{
  readTheHomeworkHandout( student );
  askQuestions( TA, student );
}
while ( isStillAwake( student ) )
  study(student);

The do-while Statement

Natural for doing an action then testing for completion before repetition

do
  turnIgnition( car );
while (! started( car ) );
do
  pressANumber( phone );
while (! haveAConnection( phone ) );
do
{
  readTheHomeworkHandout( student );
  askSomeQuestions( TA, student );
} while ( ! understands( student, materialForWeek( w ) ) );
do
  eat( person, pintOfIceCream );
while ( !isSick( person ) );

Nested loops

EG // print out a calendar

const int JAN = 1, DEC = 12;
int main()
{
  for ( int y = 2000; y <= 2010; y++ )
    for ( int m = JAN; m <= DEC; m++ )
    {
      for ( int d = 1; d <= DAYS_PER_MONTH; d++ )
        cout << m << "/" << d "/" << y << ' ';
      cout << endl;
    }
}

Loop Caveats

loop control variable is only in scope over loop body

for (int i = 0; i < 10; i++ )
  cout << i;
cout << i; /// i is no longer in scope

some errors may cause an infinite loop

for (int i = 0; i < 10; i+1 ) /// i+1 is not advancing
  cout << i;
...
int i; /// may forget to initialize
while ( i < 10 )
  cout << i; /// not advancing!

some errors may cause wrong values for i or incorrect number of loops

for (int i = 0; i <= 10; i++ ) /// wrong < operator
  cout << i;
...
for (int i = 1; i < 10; i++ ) /// wrong initial value
  cout << i;

Simple Arrays

a fixed size, single-dimensional array of elements of the same type
EG an array of three integers
```
int a[3] = {0, 1, 2};
```

processed naturally with a for loop

for ( int i = 0; i < 3; i++ )
  a[i] += 5; // add 5 to each element of array a

can access individual elements directly

a[2] = a[0]; // assign value at a[0] into memory at a[2]

can print them out

for ( int i = 0; i < 3; i++ )
  cout << a[i] << endl;

you must keep track of the array size

const int A_LENGTH = 3;
int main()
  int a[A_LENGTH];
  ...
    for ( int i = 0; i < A_LENGTH; i++ )
      out << a[i] << endl;

Extended Example

EG a TimeSheet

 #include <iostream.h>
const int SUN = 0;
const int MON = 1;
const int TUE = 2;
const int WED = 3;
const int THU = 4;
const int FRI = 5;
const int SAT = 6;
const int DAYS_PER_WEEK = 7;
void initialize( int hoursWorked[] )
{
  for ( int i = 0; i < DAYS_PER_WEEK; i++ )
    hoursWorked[i] = 0;
}
void print( ostream & out, int hoursWorked[] )
{
  for ( int i = 0; i < DAYS_PER_WEEK; i++ )
    out << "On day "
      << i
      << " worked "
      << hoursWorked[i]
      << " hours\n";
}
void recordHours(int hoursWorked[], int i, int hours)
{
  hoursWorked[i] = hours;
}
int totalHours( int hoursWorked[] )
{
  int totalHours = 0;
  for ( int i = 0; i < DAYS_PER_WEEK; i++ )
    totalHours += hoursWorked[i];
  return totalHours;
}
void reportTotals( int hoursWorked[] )
{
  print( cout, hoursWorked );
  cout << "Worked "
     << totalHours( hoursWorked )
     << " total hours this week\n";
}
int main()
{
  int hoursWorked[DAYS_PER_WEEK];
  initialize(hoursWorked);
  recordHours(hoursWorked, MON, 8);
  recordHours(hoursWorked, TUE, 9);
  recordHours(hoursWorked, WED, 6);
  recordHours(hoursWorked, THU, 9);
  recordHours(hoursWorked, FRI, 4);
  reportTotals(hoursWorked);
  return 0;
}

Character Arrays (AKA character strings)

character strings are arrays of characters terminated by '\0'
tricky thing is you need an extra element for the terminator

Three examples (of the string containing "abc")

char s1[4] = {'a','b','c','\0'};
char s2[4] = "abc";
char s3[] = "abc";

Searching a character string for a specified character

to find the index of an element containing a specified value

int findIndexOfChar(char c, char s[])
{
  for ( int i = 0; s[i] != '\0'; i++ )
    if ( s[i] == c )
      return i;
  return -1;
}

example of use

int main()
{
  char s[] = "Hello There";
  int posT = findIndexOfChar( 'T', s );
  if ( posT == -1 )
    cout << "T is not in " << s << endl;
  else
    cout << "T is at position " << posT << endl;
  s[posT] = 'W';
  cout << s << endl; // prints: Hello Where
  return 0;
}

String Library Functions

important low-level string utilities

 #include <string.h>
int	 strlen(const char s[]);
int	 strcmp(const char s1[], const char s2[]);
char [] strdup(const char s[]);
char [] strcpy(char s1[], const char s2[]);
char [] strcat (char s1[], const char s2[]);

examples of use

int main()
{
  char s[] = "Hello";
  char t[] = "There";
  char buf[1024];
  cout << strlen(s) << ' ' << strlen(t) << endl;
  if ( strcmp(s,t) == 0 )
    cout << s << " is equal to " << t << endl;
  else
    cout << s << " is not equal to " << t << endl;
  strcpy(buf, s);
  strcat(buf, " ");
  strcat(buf, t);
  cout << buf; // prints: Hello There
  return 0;
}