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More on Program Flow 193

7

LISTING7.13 Illustrates the Null Statement in a forLoop

1: //Listing 7.13

2: //Demonstrates null statement

3: // as body of for loop

4:

5: #include <iostream>

6: int main()

7: {

8: for (int i = 0; i<5; std::cout << “i: “ << i++ << std::endl)

9: ;

10: return 0;

11: }

i: 0

i: 1

i: 2

i: 3

i: 4

The forloop on line 8 includes three statements: The initializationstatement

establishes the counter iand initializes it to 0. The conditionstatement tests for

i<5, and the actionstatement prints the value in iand increments it.

Nothing is left to do in the body of the forloop, so the null statement (;) is used. Note

that this is not a well-designed forloop: The action statement is doing far too much.

This would be better rewritten as

8: for (int i = 0; i<5; i++)

9: cout << “i: “ << i << endl;

Although both do the same thing, this example is easier to understand.

Nesting Loops ................................................................................................

Any of the loop can be nested within the body of another. The inner loop will be exe-

cuted in full for every execution of the outer loop. Listing 7.14 illustrates writing marks

into a matrix using nested forloops.

LISTING7.14 Illustrates Nested forLoops

1: //Listing 7.14

2: //Illustrates nested for loops

3: #include <iostream>

4:

5: int main()

6: {

7: using namespace std;

OUTPUT

ANALYSIS