1 / 19

‘C’ in a Nutshell

‘C’ in a Nutshell. A “crash course” in C... ...with designs for embedded systems by J. S. Sumey. II. Program Flow Control. - specifies order in which program computations are performed. Control Flow Constructs. statements & blocks decision: if-else selection: switch

ide
Download Presentation

‘C’ in a Nutshell

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. ‘C’ in a Nutshell A “crash course” in C... ...with designs for embedded systems by J. S. Sumey

  2. II. Program Flow Control - specifies order in which program computations are performed

  3. Control Flow Constructs • statements & blocks • decision: if-else • selection: switch • looping: do-while, while, for • loop control: break, continue • labels and goto 'C' in a Nutshell by J. Sumey

  4. Statements & blocks • statements are terminated with a semicolon • ex: x = 0; printf(...); • blocks are groups of statements bounded by braces • ex: { int i; for (i = 0; i < 10; i++) ... } • a block is valid anywhere a single statement is valid, useful for ‘very’ local variables 'C' in a Nutshell by J. Sumey

  5. Decision: 1- or 2-way • if-else used for conditional execution • ex: if (expr)stmt1elsestmt2 • executes stmt1 if expr is true (non-zero), stmt2 if expression is false (equal to 0) • ‘else stmt2’ is optional • nested ifs: else is always paired with most recent elseless-if; use braces to override this! 'C' in a Nutshell by J. Sumey

  6. if-elses may be cascaded for multi-way decisions first true expr causes its stmt to execute and terminate whole chain optional final else part handles “none of the above” (default) case ex:if (expr1)stmt1else if (expr2)stmt2else if (expr3)stmt3...elsestmt0 Decision: multi-way 'C' in a Nutshell by J. Sumey

  7. multi-way decision based on a single expression against a number of constant values matching const value causes execution to start at that stmt use break within each stmt group to prevent “fall-thru” optional default: part executes if no match is found ex:switch (expr){ caseconst1: stmts1caseconst2: stmts2...default: stmts0} Selection 'C' in a Nutshell by J. Sumey

  8. repeats a statement or block until expression is no longer true loop body always executes at least once(posttest loop) equivalent to a “repeat-until” construct of other languages ex:dostmtwhile (expr); or:do {stmt1 stmt2 ...} while (expr); Looping: do-while loop 'C' in a Nutshell by J. Sumey

  9. repeats a statement or block as long as the expression is true loop body may execute zero times!(pretest loop) more commonly used than do-while ex:while (expr)stmt or:while (expr){stmt1 stmt2 ...} Looping: while loop 'C' in a Nutshell by J. Sumey

  10. is a fancy while-do typically used when number of iterations is known in advance expr1 typically used as initializer, expr2 for test condition, expr3 for loop maintenance expressions may be “complex”; are also optional ex:for (expr1; expr2; expr3)stmt same as:expr1;while (expr2){stmt expr3;} Looping: for loop update part terminal test initializer 'C' in a Nutshell by J. Sumey

  11. Example: for loop • display the numbers from 1 to 49 with their “mirrors” about 50 in two columns; also compute & display their sum int i, sum;for (sum = 0, i = 1; i < 50; sum += i++) printf( “%i %i\n”, i, 100-i );printf( “sum = %i\n”, sum ); 'C' in a Nutshell by J. Sumey

  12. causes early exit from a loop or switch useful for detecting abnormal conditions in loops or to prevent “fall-thru” in switch blocks ex:switch (result){ case -1: do_neg(); break; case 0: do_zero(); break; case +1: do_pos();} Loop control: break 'C' in a Nutshell by J. Sumey

  13. forces next iteration of a for, while or do-while loop useful for bypassing a ‘complicated’ loop ex: find the sum of the positive elements of a 10-element array ex:sum=0;for (i=0; i<10; i++){ if (a[i] < 0) continue; sum += a[i];} Loop control: continue 'C' in a Nutshell by J. Sumey

  14. typically considered “bad practice” and is avoided however, useful in the main processing loop of embedded systems syntax: gotolabel; label names follow same rules as variables, followed by colon ex:main(){ MainLoop: read_sensors(); do_calculations(); control_outputs(); goto MainLoop;} Labels & goto 'C' in a Nutshell by J. Sumey

  15. III. Functions - allow large, complicated problems to be broken down into smaller, simpler pieces

  16. Function basics • C programs are typically composed of many small, well-defined functions • a typical program is simply a set of related variable and function definitions • one ‘special’ function named main() is treated as the ‘top’ of the program • functions may accept zero or more arguments and return zero or one result value 'C' in a Nutshell by J. Sumey

  17. Function syntax • function definition form: return-val-type function-name (argument_declarations ){ declarations and statements} • only function_name is required • ex: useless() { } 'C' in a Nutshell by J. Sumey

  18. Return values • by default (i.e. return type not specified), a C function returns an integer • ex: int compute_average() ... • use return statement to exit function • ex: return expression; • can return other types instead • char, float, double, or pointer to a complex type • a function with no return value should be declared as returning a void type • ex: void do_calculations() ... • a function having no arguments should be declared as such (some compilers enforce this!) • ex: void do_calculations(void)… 'C' in a Nutshell by J. Sumey

  19. Example function a function to return 1 if a specified year is a leap year, 0 if not int leapyear( int y ){ return ( y%4 == 0 && y%100 != 0 || y%400 == 0 );}main(){ int yr = 2016; printf( “%i is %sa leapyear”, yr, leapyear(yr) ? “” : “not ”);} 'C' in a Nutshell by J. Sumey

More Related