Programming Tutorials

continue and break statements in C++

By: Priya in C++ Tutorials on 2007-09-09  

At times you'll want to return to the top of a while loop before the entire set of statements in the while loop is executed. The continue statement jumps back to the top of the loop.

At other times, you may want to exit the loop before the exit conditions are met. The break statement immediately exits the while loop, and program execution resumes after the closing brace.

The following C++ program demonstrates the use of these statements. This time the game has become more complicated. The user is invited to enter a small number and a large number, a skip number, and a target number. The small number will be incremented by one, and the large number will be decremented by 2. The decrement will be skipped each time the small number is a multiple of the skip. The game ends if small becomes larger than large. If the large number reaches the target exactly, a statement is printed and the game stops.

The user's goal is to put in a target number for the large number that will stop the game.

break and continue.

1:    // \
2:    // Demonstrates break and continue
3:
4:    #include <iostream.h>
5:
6:    int main()
7:    {
8:      unsigned short small;
9:      unsigned long  large;
10:      unsigned long  skip;
11:      unsigned long target;
12:      const unsigned short MAXSMALL=65535;
13:
14:      cout << "Enter a small number: ";
15:      cin >> small;
16:      cout << "Enter a large number: ";
17:      cin >> large;
18:      cout << "Enter a skip number: ";
19:      cin >> skip;
20:      cout << "Enter a target number: ";
21:      cin >> target;
22:
23:    cout << "\n";
24:
25:     // set up 3 stop conditions for the loop
26:      while (small < large && large > 0 && small < 65535)
27:
28:      {
29:
30:        small++;
31:
32:         if (small % skip == 0)  // skip the decrement?
33:         {
34:           cout << "skipping on " << small << endl;
35:           continue;
36:         }
37:
38:         if (large == target)    // exact match for the target?
39:         {
40:           cout << "Target reached!";
41:           break;
42:         }
43:
44:         large-=2;
45:      }                   // end of while loop
46:
47:      cout << "\nSmall: " << small << " Large: " << large << endl;
48:    return 0;
49: }
Output: Enter a small number: 2
Enter a large number: 20
Enter a skip number: 4
Enter a target number: 6
skipping on 4
skipping on 8

Small: 10 Large: 8

Analysis: In this play, the user lost; small became larger than large before the target number of 6 was reached.
On line 26, the while conditions are tested. If small continues to be smaller than large, large is larger than 0, and small hasn't overrun the maximum value for a small int, the body of the while loop is entered.

On line 32, the small value is taken modulo the skip value. If small is a multiple of skip, the continue statement is reached and program execution jumps to the top of the loop at line 26. This effectively skips over the test for the target and the decrement of large.

On line 38, target is tested against the value for large. If they are the same, the user has won. A message is printed and the break statement is reached. This causes an immediate break out of the while loop, and program execution resumes on line 46.

 

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NOTE: Both continue and break should be used with caution. They are the next most dangerous commands after goto, for much the same reason. Programs that suddenly change direction are harder to understand, and liberal use of continue and break can render even a small while loop unreadable.

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The continue Statement

continue; causes a while or for loop to begin again at the top of the loop. Example

if (value > 10)
     goto end;

if (value < 10)
     goto end;

cout << "value is 10!";

end:

cout << "done";

The break Statement

break; causes the immediate end of a while or for loop. Execution jumps to the closing brace. Example

while (condition)
{
    if (condition2)
        break;
    // statements;
}