Statements

  • Statement = a command issued to the computer to "do something"

      • Statement is the unit of execution in a programming language

  • In Java:

      • A statement must be contained inside some method

  • All (procedural) programming languages have these 3 types of statements:

      • Assignment
      • Conditional
      • Loop

Assignment statement

  • Syntax: 

      variable = expression ;

    Examples: 

      x = 4;     // Store the value 4 in variable x

  x = x + 1; // Read the value in variable x, add 1 to it,       
             // then store result in variable x

  • Notes:

      • Variables on the right hand side of the = operator are read (= accessed)

      • The variable on the left hand side of the = operator is written (= updated)

Selection statements

  • If-statement 

        if ( condition )          if ( condition )
       one-statement;         {
                                 statement1;
				 statement2;
				 ...
			      }

  • If-else-statement 

        if ( condition )          if ( condition )
       one-statement;         {
    else                         statement1;
       one-statement;		 statement2;
				 ...
			      }
			      else
			      {
			         statement3;
				 statement4;
				 ...
			      }

Multi-way selection statements

  • Switch-statement 

            Switch ( integer-expression )
        {
           case intVal1: statement1-1;
                         statement1-2;
			 ...
			 break;

           case intVal2: statement2-1;
                         statement2-2;
			 ...
			 break;

	   ...

           default:      statementD-1;  // Optional clause !!!      
                         statementD-2;
			 ...
			 break;
        }

Loop statements

  • While-loop 

      while ( condition )       while ( condition )
     one-statement;         {
			       statement1;
			       statement2;
			       ...
			    }

  • For-loop 

      for ( init ; term-cond ; incr )
  {
      statement1;
      statement2;
      ...
  }

  • do-while-loop is rarely used...

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Trace result: 

      Statements                    i     sum
 ===================       =================

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Initialization: 

      Statements                    i     sum
 ===================       =================
   sum = 1                             1
   i   = 0                      0

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 1: 

      Statements                    i     sum
 ===================       =================
                                0      1
   i <= 5?   T                     
   sum = sum + i++                     1 + 0 = 1
                                1

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 2: 

      Statements                    i     sum
 ===================       =================
                                1      1
   i <= 5?   T                     
   sum = sum + i++                     1 + 1 = 2
                                2

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 3: 

      Statements                    i     sum
 ===================       =================
                                2      2
   i <= 5?   T                     
   sum = sum + i++                     2 + 2 = 4
                                3

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 4: 

      Statements                    i     sum
 ===================       =================
                                3      4
   i <= 5?   T                     
   sum = sum + i++                     4 + 3 = 7
                                4

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 5: 

      Statements                    i     sum
 ===================       =================
                                4      7
   i <= 5?   T                     
   sum = sum + i++                     7 + 4 = 11
                                5

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 6: 

      Statements                    i     sum
 ===================       =================
                                5      11
   i <= 5?   T                     
   sum = sum + i++                    11 + 5 = 16
                                6

Loop tracing

  • Trace the execution of the following loop: 

        int sum = 1;

    for ( int i = 0; i <= 5; sum = sum + i++ );      

    System.out.print(sum);

  • Iteration 7: 

      Statements                    i     sum
 ===================       =================
                                6      16
   i <= 5?   F                     
                                                   
   STOP