For Body

layout: default title: for Loop Body

The first statement or first code block after a for statement is considered its body.

code block¶

Anything in curly braces { }. This defines scope, which is where a variable is available. For example...

int i = 0;
for (i = 0; i < 5; i++) {
  int iTimesTwo = 2 * i;
  System.out.println(iTimesTwo);
}
// iTimesTwo is no longer available, i.e. "out of scope"
System.out.println("i is still in scope with value " + i);

// Curly braces are required for multiple loop body statements
for (initialization; termination; increment) {
  loop body
  more loop body
}

Making the loop body a code block { } is preferred, even if the body is only one statement. * It makes the code more readable and prevents error.

  // Preferred...
  for (int i=0; i<5; i+=1){
    System.out.println(i);  
  }

  // Works...
  for (int i=0; i<5; i+=1)
    System.out.println(i);

  // Misleading... is the second statement part of the for loop?
  for (int i=0; i<5; i+=1)
    System.out.print(i);
    System.out.print("\n");

  // Bug!
  for (int i=0; i<5; i+=1); // <-- ; is the first statement
    System.out.print(i);   // <-- does not compile, i is out of scope

Practice Exercise¶

You can declare or initialize multiple variables in the initialization section of a for loop, but you can't do both.

// Legal
for (int i = 0, j = 1; i + j < 12; i++, j++){  
  // ...
}

// Illegal - this redeclares j rather than initializing it in the for loop
int j;
for (int i = 0, j = 1; i + j < 12; i++, j++){  
  // ...
}
// Compiler error: Duplicate local variable j

Drill¶

ForLoops/src/drills/ForLoopBody.java * Write a for loop to print the numbers 10 to 1 on the screen. * Write a for loop to find the sum of the values 1 to 10. Print the sum to the screen. * Write a for loop to print the values 1 to 5. Output should be comma-separated: 1, 2, 3, 4, 5. Hint: the loop will need to check which iteration it is on to prevent a comma showing after 5.

Forloops/src/drills/ForLoopBody2.java * The for loops in the block comment have errors. Copy each loop and paste below the block comment. Fix the code so that it can compile.

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