4.7. Break and Continue

It is sometimes convenient to be able to exit from a loop other than testing at the top or bottom. The break statement provides an early exit from for, while, and do, just as from switch. A break causes the innermost enclosing loop or switch to be exited immediately.

The following function, trim, removes trailing blanks, tabs, and newlines from the end of a string, using a break to exit from a loop when the rightmost non-blank, non-tab, non-newline is found.

/*trim: remove trailing blanks, tabs, newlines*/
int trim(char s[])
  int n;
  for(n = strlen(s) -1; n >= 0; n--)
    if(s[n] != '' && s[n] != '\t' && s[n] != '\n')
  s[n+1] = '\0';
  return n;

Strlen returns the length of the string. The for loop starts at the end and scans backwards looking for the first character that is not a blank or tab or newline. The loop is broken when one is found, or when n becomes negative (that is, when the whole string has been scanned)

The continue statement is related to break, but less often used; it causes the next iteration of the enclosing for, while, or do loop to begin  In the while and do, this means that the test part is executed immediately; in the for, control passes to the increment step. The continue statement applies only to loops, not to switch. A continue inside a switch inside a loop causes the next loop iteration.

As an example, this fragment processes only non-negative elements in the array a; negative values are skipped.

for(i = 0; i < n; i++)
  if(a[i] < 0)/*skip negative elements*/
  .../*do positive elements*/

NOTE!  This  chapter does not include exercises but it is important that the student does these examples above.