CODEWITHSUNDEEP
javafor-loopcurly-braces
zodiac645
zodiac645

Reputation: 191

for loop without braces in java

I wonder why this two following codes give different results;

for(i = 1, j = 0; i < 10; i++) {
    j += i;
    System.out.println(i);
}

This one gives the numbers between 1 included and 10 excluded. 

for(i = 1, j = 0; i < 10; i++)
    j += i;
System.out.println(i);

However this one gives 10. I could not get the logic of this;

for()
do_something;
do_something_else;

Upvotes: 1

Views: 16018

Answers (6)

tbs
tbs

Reputation: 480

In addition to the above answers, the immediate statement could in the form of another loop. This inner loop could have multiple statements. But still for the outer loop, it is known to be a single statement as it is referred as a single statement.

For example,

for(int i=1; i<3; i++) 

  for(int j=1; j<3; j++){
    System.out.println(i + " " + j);      
    System.out.println("still inside inner loop");
  }

System.out.println("out of inner and outter");
System.out.println("out of inner and outter");

Output,

1 1
still inside inner loop
1 2
still inside inner loop
2 1
still inside inner loop
2 2
still inside inner loop
out of inner and outter
out of inner and outter

Upvotes: 0

Naman
Naman

Reputation: 31888

That is because the default scope of an iteration in your case is the only line following it, something equivalent to - 

for(i=1, j=0;i<10;i++) {
    j += i;
}
System.out.println(i);

Hence the entire loop is iterated and since after that the value of i==10, that is your output in the second case.

In the first case, it's pretty obvious that the value is printed with each iteration and hence 1 to 9(less than 10) :

for(i=1, j=0;i<10;i++){
    j += i;
    System.out.println(i);
}

Upvotes: 4

Andreas
Andreas

Reputation: 159106

The for loop, the while loop, and the if statement (ignoring else) all control a single Statement:

for ( [ForInit] ; [Expression] ; [ForUpdate] ) Statement

for ( {VariableModifier} UnannType VariableDeclaratorId : Expression ) Statement

while ( Expression ) Statement

if ( Expression ) Statement

That statement may be a Block, i.e. braces {} with multiple statements.

So, this code is all the same:

for(i=1, j=0;i<10;i++)
j += i;
System.out.println(i);

for(i=1, j=0;i<10;i++)
    j += i;
    System.out.println(i);

for(i=1, j=0;i<10;i++)
    j += i;
System.out.println(i);

for(i=1, j=0;i<10;i++) {
    j += i;
}
System.out.println(i);

The first two are very bad, because they hide (misrepresent) the code structure.

Many people advocate always using blocks, to prevent confusing and coding errors.

Upvotes: 10

J-Alex
J-Alex

Reputation: 7107

The first statement contains a block of code. A block of code is handled as one unit.

To create a block of code you should insert statements between curly braces.

loop and conditional expressions are handling only the first statement under them, if no block of code specified.

Therefore:

// Both statements handled 10 times
for(i = 1, j = 0; i < 10; i++) {
    j += i;
    System.out.println(i);
}

// Only the first statement handled 10 times, the second one is out of scope of the loop
for(i = 1, j = 0; i < 10; i++)
    j += i;
System.out.println(i);

Upvotes: 1

phico
phico

Reputation: 1403

Loop without braces apply only to the next statement

So :

 for(i=1, j=0;i<10;i++)
    j += i;
System.out.println(i);

is equivalent to : 

 for(i=1, j=0;i<10;i++){
        j += i;
 }
    System.out.println(i);

i is defined out of loop scope and is incremented after the last loop so it has value of 10

Upvotes: 1

3141
3141

Reputation: 148

In the second example, the output is outside the for loop. A for loop without curly brackets only includes the following statement.

Upvotes: 4

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