Chapter 5 Repetition while dowhile and for loops

Chapter 5 - Repetition Ø while, do-while, and for loops revisited Ø infinite loops Ø comma operator Ø break statement Ø continue statement

the WHILE loop Ø The general form of the while loop is while (expression) statement; Ø if the expression is true, the program executes the body of the loop - in this case the single statement Ø The test is performed first - if it is false the body is NOT executed even once.

the DO-WHILE loop Ø The general form of the do-while loop is do { statement; } while (expression); Ø We will always use the braces in this class, though they are not required for a single statement. Ø The test is made at the end of the loop, so the loop is always executed at least once.

the FOR loop Ø The general form of the for loop is for (expression 1; expression 2; expression 3) statement; – the for loop is more compact, but equivalent to: expression 1; while (expression 2) { statement; expression 3; }

Infinite loops Ø We will see examples of why infinite loops can be useful soon. Here’s how to create them: – while (1) {. . . – do {. . } while (1); – for (i=0; ; i++) {

The COMMA operator Ø The comma operator is used to combine a number of expressions into one. Ø General form: expression 1, expression 2, . . . , expressionm; Ø expression 1 is evaluated first, expressionm is done last (left-to-right) Ø Result of the whole expression is the result and type of rightmost expression.

The COMMA operator continued Ø a=(b=3, c=b+4); assigns 3 to b and 7 to c and a Ø Possibly the most common use of the comma operator is in for expressions: for(n=exp_x=term=1; n<100; term*=x/n++, exp_x+=term); for(sum=0. 0, i=0; i<MONTHS; sum+=atoi(gets(buff)), i++) printf(“Month %dn”, i);

The BREAK statement Ø Already discussed in Chapter 4 in conjunction with the switch statement. Ø Break can also be used to terminate a loop: for (sum=0, count=0; ; count++){ /* infinite loop */ printf(“Enter a number: “); if (scanf(“%d”, &num)==EOF) break; sum+= num }

The BREAK statement continued Ø in a nested loop, break only terminates the inner most loop - NOT all loops: while (i<5) { while (j<3) { if (i==5) break; /* jump out of inner most loop */. . . }. . . /* execution begins here after break */ }

The CONTINUE statement Ø The continue statement immediately forces the statements after the continue statement and up to the end of the loop to be skipped and a new iteration of the loop to begin. Ø Unlike the break statement: – the loop is not terminated. – the continue statement serves no useful purpose in a switch statement (unless it is imbedded in a loop).

The CONTINUE statement ctd. Ø The general form in a for loop is: for (expression 1; expression 2; expression 3) {. . . if (expr) continue; . . . /* these statements skipped if expr is true */ }

To continue or not to continue. . . do { if (x==y) { statement 1; continue; } statement 2; statement 3; } while (. . . ); do { if (x==y) statement 1; else { statement 2; statement 3; } } while (. . . );

Program 5. 1 - the “bubble” sort Ø read in an array of numbers and sort them from high to low

Program 5. 1 - specification – start – declare variables – prompt for input – read in an array of numbers, stop if EOF – print numbers in original order – sort the numbers from high to low – print sorted numbers at end of each inner loop – stop

Program 5. 1 - part 1 /* perform a bubble sort of an integer array from high to low*/ #include <stdio. h> int main(int argc, char *argv[]) { int num[100], i, j, temp, count; // input all of the integers that we are going to sort for(count=0; count<100; count++) { printf("Enter an integer # %i (0 to exit): ", count+1); if (scanf("%d", &num[count])==EOF) break; if (num[count]<=0) break; }

Program 5. 1 - part 2 // print array before we start to sort printf("nn. The unsorted array is: n"); for(i=0; i<count; i++) printf("%c %d", i%10? ' ': 'n', num[i]); // sort for(j=0; j<count-1; j++) { for(i=j+1; i<count; i++) if(num[i]>num[j]) { temp=num[i]; num[i]=num[j]; num[j]=temp; } }

Program 5. 1 - part 3 // finished sort high to low; print results printf("nn. The SORTED array is: n"); for(i=0; i<count; i++) printf("%c %d", i%10? ' ': 'n', num[i]); printf("nn"); return 0; }

Program 5. 2 Ø Write a code to read in the value of resistance, inductance, and a range and number of frequencies and calculate the voltage divider ratio as a function of frequency.

Voltage Dividers • Have many uses: – For measuring large voltages via a calibrated divider – For simplifying some circuit calculations – As filters, either high-pass, low-pass, band-pass or band-notch – The circuit for program 5. 2 is an example of a high -pass filter

High-pass filter

Program 5. 2 - specification – start – declare variables, initialize constants – prompt for resistance, inductance, etc. – read resistance, inductance, etc. – start at lowest frequency – compute divider ratio and print – increment frequency logarithmically – if frequency less than maximum frequency, repeat last two steps – stop

Program 5. 2 - part 1 // Frequency response // // Written by W. Lawson // // last modified 30 Oct 2014 // #include <stdio. h> #include <math. h> #define PI 3. 141592654 // /* A program to evaluate the voltage divider rule for an RL circuit as a function of frequency with lineqr and nonlinear increments */ // int main(void) {

Program 5. 2 - part 2 int i=0, num_freq; double r, l, freq, temp, freq_min, freq_max, vrat, freqlin, vratlin; printf("enter resistance (ohms)"), scanf("%lf", &r); printf("enter inductance (m. H)"), scanf("%lf", &l); printf("enter minimum frequency (k. Hz)"), scanf("%lf", &freq_min); printf("enter maximum frequency (k. Hz)"), scanf("%lf", &freq_max); printf("enter number of frequency points"), scanf("%d", &num_freq); printf("n. Frequency (k. Hz) t. Voltage Rationn"); printf("nnn Nonlinear Spacing tt Linear spacingnn");

Program 5. 2 - part 3 while (i<num_freq) { // nonlinear spacing freq=freq_min*pow(freq_max/freq_min, (float)i/(num_freq-1)); temp=2. *PI*freq; vrat=temp/sqrt(r*r+temp*temp); // linear spacing freqlin=freq_min+(freq_max-freq_min)*i/(num_freq-1); temp=2. *PI*freqlin; vratlin=temp/sqrt(r*r+temp*temp); // print results printf(" %f tt %fn", freq, vrat, freqlin, vratlin); i++; } return 0; }