vb.net barcode font 6: Controlling Your Program s Flow in Java

Generator Data Matrix in Java 6: Controlling Your Program s Flow

CHAPTER 6: Controlling Your Program s Flow
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loopTester starts off with the standard #include. main() defines a counter variable i and sets i to 0:
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#include <stdio.h> int main (int argc, const char * argv[]) { int i; i = 0; main() then enters a while loop: while ( i++ < 4 ) printf( "while: i=%d\n", i );
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The loop executes four times, resulting in this output:
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while: while: while: while: i=1 i=2 i=3 i=4
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Do you see why If not, go through the loop yourself, calculating the value for i each time through the loop. Remember, since we are using postfix notation (i++), i gets incremented after the test is made to see if it is less than 4. The test and the increment happen at the top of the loop, before the loop is entered. Once the loop completes, we print the value of i again:
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printf( "After while loop, i=%d.\n\n", i );
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Here s the result:
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After while loop, i=5.
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Here s how we got that value. The last time through the loop (with i equal to 4), we go back to the top of the while loop, test to see if i is less than 4 (it no longer is), and then do the increment of i, bumping it from 4 to 5. OK, one loop down, two to go. This next loop looks like it should accomplish the same thing. The difference is that we don t do the increment of i until the bottom of the loop, after we ve been through the loop once already.
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for ( i = 0; i < 4; i++ ) printf( "first for: i=%d\n", i );
CHAPTER 6: Controlling Your Program s Flow
As you can see by the output, i ranges from 0 to 3 instead of from 1 to 4.
first first first first for: for: for: for: i=0 i=1 i=2 i=3
Once we drop out of the for loop, we again print the value of i:
printf( "After first for loop, i=%d.\n\n", i );
Here s the result:
After first for loop, i=4.
This time, the while loop ranged i from 1 to 4, leaving i with a value of 5 at the end of the loop. The for loop ranged i from 0 to 3, leaving i with a value of 4 at the end of the loop. So how do we fix the for loop so it works the same way as the while loop Take a look:
for ( i = 1; i <= 4; i++ ) printf( "second for: i=%d\n", i );
This for loop started i at 1 instead of 0. It tests to see if i is less than or equal to 4 instead of just less than 4. We could also have used the terminating expression i < 5 instead. Either one will work. As proof, here s the output from this loop:
second second second second for: for: for: for: i=1 i=2 i=3 i=4
Once again, we print the value of i at the end of the loop:
printf( "After second for loop, i=%d.\n", i ); return 0; }
Here s the last piece of output:
After second for loop, i=5.
This second for loop is the functional equivalent to the while loop. Take some time to play with this code. You might try to modify the while loop to match the first for loop. By far, the while and for statements are the most common types of C loops. For completeness, however, we ll cover the remaining loop, a little-used gem called the do statement.
CHAPTER 6: Controlling Your Program s Flow
The do Statement
The do statement is a while statement that evaluates its expression at the bottom of its loop, instead of at the top. Here s the pattern a do statement must match:
do statement while ( expression ) ;
Here s a sample:
i = 1; do { printf( "%d\n", i ); i++; } while ( i < 3 ); printf( "We are past the do loop." );
The first time through the loop, i has a value of 1. The printf() prints a 1 in the console window, and the value of i is bumped to 2. It s not until this point that the expression ( i < 3 ) is evaluated. Since 2 is less than 3, a second pass through the loop occurs. During this second pass, the printf() prints a 2 in the console window, and the value of i is bumped to 3. Once again, the expression ( i < 3 ) is evaluated. Since 3 is not less than 3, we drop out of the loop to the second printf(). The important thing to remember about do loops is this: since the expression is not evaluated until the bottom of the loop, the body of the loop (the statement) is always executed at least once. Since for and while loops both check their expressions at the top of the loop, either can drop out of the loop before the body of the loop is executed. Let s move on to a completely different type of statement, known as switch.
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