CSCI 130 Advanced Program Control Chapter 8

Program Controls so far for loop while loop do…while loop

The break statement Can be placed inside the body of a loop When break is encountered, loop is exited (regardless of the condition) Execution passes to first statement outside the loop A break inside a nested loop only causes exiting of the innermost loop

break example for (count = 0; count <= 10; count ++) { if (count == 5) break; } Without break loop iterates 11 times With break, loop stops during 6th iteration

Another break example Write a for loop that will search a 10 element array for the value 12. for (i = 0; i < 10; i ++) {//for written with no break if (arrayName[i] = 12)//this is less efficient foundFlag = ‘Yes’;//Entire array always }//searched for (i = 0; i < 10; i++) {//for written with break if (arrayName[i] = 12) {//more efficient foundFlag = ‘Yes’;//if 12 is first element break;//than loop only entered }//once }

The continue statement Can be placed within the body of a loop When continue encountered, control passes to the next iteration of the loop Statements between continue and end of loop not executed Significantly different than break

Example of continue for (count = 0; count <= 10; count ++) { if (count == 5) continue; printf(“%d ”, count); } Loop iterates 11 times, with or without continue statement Output: –5 is skipped

Another continue example Write the code to check an array of 100 elements. Write out only those elements in the array that are not prime for (i = 0; i < 100; i++) { if (numIsPrime(arrayName[i])) continue; printf(“\n%d”, arrayName[i]); } Note: numIsPrime will return a positive number for primes

The goto statement C’s unconditional branching statement goto and target statement must be in the same function goto can always be performed using better structures (do…while, etc.) NEVER use a goto

Example of a goto void main ( ) { int count= 3; printf("Before any goto %d\n", count); goto location0; printf("This will not print out\n"); location0: ; printf("At location 0\n"); location1: ; printf("At location 1\n"); }

Strong suggestion about goto NEVER USE A GOTO

Infinite Loops Condition will never be evaluated as false Theoretically would run forever Avoid infinite loops

Examples of an infinite loop for (i = 0; i < 10; i+1)//i+1 does not change printf(“%d”, i);//the value of i while ( i < 10) {//Programmer thinks printf(“%d”, i);//i always starts greater i-=1;//than 10 } for (i = 1; i !=10; i +=2)//Printing out odd ints printf(“%d”, i);//up to 10?

The switch statement Most flexible program control statement Program control based on an expression with more than 2 possible values

Referencing elements in an array General form of switch statement: switch(expression) { case template1: statements; case template2: statements; … case templaten: statements; default: statements; }

Concrete example of switch switch(i) { case 1: printf(”The number is 1”); case 2: printf(“The number is 2”); case 3: printf(”The number is 3”); default: printf(”The number is not 1, 2, or 3"); }

Evaluation of a switch statement If expression matches a template, control passes to first statement within that template If no match, control passes to first statement within default If no match and no default, control passed to first statement after switch structure

Output of switch statement switch(i) { case 1: printf(”The number is 1\n”); case 2: printf(“The number is 2\n”); case 3: printf(”The number is 3\n”); default: printf(”The number is not 1, 2, or 3\n"); } If i = 1 Output: The number is 1 The number is 2 The number is 3 The number is not 1, 2, or 3

Correct way to code a switch switch(i) { case 1: printf(”The number is 1\n”); break; case 2: printf(“The number is 2\n”); break; case 3: printf(”The number is 3\n”); break; default: printf(”The number is not 1, 2, or 3\n"); }

System functions All within stdlib.h file (must be included) exit( ) –terminates execution atexit( ) –performs functions at program termination system( ) –executes operating system commands

exit ( ) function Terminates program execution #include void main ( ) { char i; exit(0); printf("Enter a character");//These statements will scanf("%c", &i);//not be executed }

exit ( ) function continued If 0 is passed into function it means program executed normally If 1 is passed into function it means program abnormally terminated stdlib.h has two symbolic constanst: –#define EXIT_SUCCESS 0 –#define EXIT_FAILURE 1 can call exit(EXIT_SUCCESS) can call exit(EXIT_FAILURE)

atexit ( ) function Specifies one (or more) functions that are automatically executed at termination time Up to 32 functions can be registered in this way Executed in reverse order

atexit( ) function continued #include void cleanup(); void cleanupLast(); void main ( ) { char i; atexit(cleanupLast); atexit(cleanup); printf("Enter a character"); scanf("%c", &i); }

system ( ) function Executes operating system commands Example: system(“c:\dir *.exe”); Must capture any output in a file –will not open up another console –will not print to current console Can execute any command line system(“c:\winnt\system32\notepad.exe”);

system( ) does not work in CW system( ) function does not work in Code Warrior Help states: “The system() function is an empty function that is included in the Metrowerks stdlib.h to conform to the ANSI C Standard Library specification.”