What's wrong with this For loop?

Question

I can't get this program to count the spaces, I have a feeling there is a logic error in the loop, but I am too inexperienced to figure it out myself. Any tips?

System.out.print("Enter a string: ");
String myString = keyboard.next();
int numBlanks = 0;

//find string length
int length = myString.length() - 1;
System.out.println("length " + length);

for(int sequence = 0; sequence >= length; ++sequence);
{

    if(myString.charAt(length)==' ')
    {
        numBlanks += 1;
        length -= length;
    }
    else 
        length -= length;

}

Answer 1

There are few bugs I can see:

Semicolon at the end of for loop. Remove it.

Next

sequence >= length

should be

sequence <= length

and

if(myString.charAt(length)==' ')

should be

if(myString.charAt(sequence)==' ')

and you need to change length at all as you are already changing sequence.

So we get:

for(int sequence = 0; sequence <= length; ++sequence) {

    if(myString.charAt(sequence)==' ') {
        numBlanks += 1;
    }
}

Answer 2

sequence >= length is spoken aloud as "sequence is greater than or equal to length." It is initialized to zero. When will it be greater than or equal to length?

Answer 3

First issue:

change

for(int sequence = 0; sequence >= length; ++sequence);

to

for(int sequence = 0; sequence <= length; ++sequence);  //flipped >= to <=

Second issue:

change

I am too inexperienced to figure it out myself.

to

This will be some good practice for debugging.  //int confidence should never be negative

:D

Answer 4

This is not the right way to scan a string.

// fixed semicolon at the end of for
for(int sequence = 0; sequence >= length; ++sequence)
{

    if(myString.charAt(length)==' ')
    {
        numBlanks += 1;
        length -= length;
    }
    else 
        length -= length;

}

1. What is this variable sequence supposed to do? Why are you incrementing it AND decrementing length?
2. When is the condition (sequence >= length) ever going to be true?
3. Why are you decrementing length by itself?

4. The if-else statement (if it were right) could've been rewritten as:

   if(myString.charAt(length)==' ')
   {
       numBlanks += 1;
   }
   length -= length;
   

I would do this:

numBlanks = 0;
for (char c : myString.toCharArray())
    if (c == ' ')
        numBlanks++;

So I don't have to mess with indices.

Answer 5

In addition to the errors others have pointed out, there are violations of convention here; you're calculating the length as n - 1, and then comparing <= (well, >=, but should be <=). Typically, unless there is very good reason, our for loops look like this:

for (int i = 0; i < n; i++) {
    ...
}

In your case, this would be expressed as:

for (int i = 0; i < myString.length(); i++) {
    ...
}

It is also conventional to stick with "i" as the loop variable, unless there's good reason to use another; in your case, "sequence" is just confusing.