Lecture #13: Statements 4

November 1, 1999

Bob Pitha

bpitha@cs.ucsd.edu

http://www-cse.ucsd.edu/classes/fa99/cse5a

review

• We’ve talked about:

– expression statements

• any valid expression with a semicolon stuck on the end

– compound statements

• one or more statements (and optional declarations) surrounded by braces

– selection statements

• if-else

• switch

– iteration statements

• while

• for

one more iteration statement: do-while

do statement while ( expression );

• A lot like the while statement

– except the expression is tested after statement, not before

– the difference is that statement is always executed at least once, even if expression is never true

• with the while statement, the body would not be executed even once in that case

do-while example

$Text Box: do { printf (“Input a positive integer: “); scanf (“%d”, &n); if (error = (n <= 0)) printf (“\nERROR: Try again!\n”); } while (error);$

jump statements: break and continue

break

• break exits a loop or a switch statement immediately

– but only from the innermost loop if it’s a nested loop

• This example code repeatedly reads a number from the keyboard and prints its square root. If the number is negative, it stops.

$Text Box: while (1) { scanf (“lf”, &x); if (x < 0.0) break; printf (”%f\n”, sqrt(x)); }$

break example

$Text Box: #include <stdio.h> #include <math.h> int main (void) { int i, j; printf (“%d\n”, 2); for (i = 3; i <= 100; ++i) { for (j = 2; j < i; ++j) { if (i % j == 0) break; if (j > sqrt(i)) { printf (%d\n”, i); break; } } } return 0; }$

continue

• continue ends the current iteration of a loop

– the control expression is evauated

– depending on the value, the next iteration starts

• Unlike break, continue doesn’t end the loop, it just skips to the end of the current cycle