Lec 6

Lecture Outline Compound Assignment Operators Increment and Decrement Operators Prefix and Postfix Increments Repetition in programs While Loop

Compound Assignment Operators counter=counter+1; time=time-1; t_time=t_time+time; sum=sum+next; n=n*(x+1); r=r/10; counter+=1; time-=1; t_time+=time; sum+=next; n*=x+1; r/=10;

Increment and Decrement Operators ++ is an increment operator that adds 1. -- is a decrement operator that subtracts 1.

Prefix and Postfix Increments ++n First add then do command. n++ First do command then add. --n First subtract then do command. n-- First do command then subtract. Example n = 4 • printf("%i", ++n); printf("%i", n++); printf("%i", --n); printf("%i", n--); 5 4 3 4

Repetition in programs What’s a loop? A control structure that repeats a group of steps in a program. What’s a loop body? The statements that are repeated in the loop. What’s a loop control variable? The variable whose value controls loop repetition. Its value determines whether the loop body is repeated.

Do you need to repeat any steps? Repetition in Programs no Do you need to repeat any steps? No loop required yes Do you Know how many times to repeat? Use one of the following : sentinel-controlled loop endfile-controlled loop input validation loop general conditional loop no yes Use a counting loop

While Statement Syntax while (loop repetition condition) statement while (loop repetition condition) {statements}

Example /* A program that print the numbers from 1 to 10*/ #include<stdio.h> int main(void) { int counter; counter=1; while (counter<=10) printf("%i\n", counter); counter++; } return(0); loop control variable loop repetition condition loop body

Loop Control Variables The loop control variable (i.e counter) MUST BE: 1. Initialized before entering the loop. 2. Tested. 3. Updated inside the loop.

Example /* A program that print the numbers from 1 to 10*/ #include<stdio.h> int main(void) { int counter; counter=1; while (counter<=10) printf("%i\n", counter); counter++; } return(0); Initialization Testing Updating

Example /* A program that prints 5 stars*/ #include<stdio.h> int main(void) { int counter; counter=0; while (counter<=4) printf("*"); counter++; } return(0); /* A program that prints 5 stars*/ #include<stdio.h> int main(void) { int counter; counter=1; while (counter<=5) printf("*"); counter++; } return(0);

Three Loops ( Each Print 3 Stars) c = 0; c = 1; c = 0; while (c <= 2) while (c <= 3) while (c < 6) { { { printf("*"); printf("*"); printf("*"); c++; c++; c = c + 2; } } }

Computing The Sum of Three Numbers #include<stdio.h> int main(void) { int next, sum; sum=0; scanf("%i", &next); sum+=next; printf("%i\n", sum); return(0); } #include<stdio.h> int main(void) { int next, sum, count; sum=0; count=1; while (count<=3) scanf("%i", &next); sum+=next; count++; } printf("%i\n", sum); return(0);

Example /* A program that prints the payroll of 8 employees */ #include<stdio.h> int main(void) {int count_emp=0; float hours, rate, pay; while (count_emp<=7) {printf("Please enter the hours: "); scanf("%f", &hours); printf("Please enter the rate: "); scanf("%f", &rate); pay=hours*rate; printf("The pay is $%.2f\n", pay); count_emp++;} printf("\nAll employees processed\n\n"); return(0);}

Exercise 1 Write a program that displays the even numbers from 0 to 10: #include<stdio.h> int main(void) {int even=0; while (even<=10) {printf("%i \n", even); even+=2;} return(0);}

Exercise 2 Write a program that produces the following output: 0 1 1 2 0 1 1 2 2 4 3 8 4 16 5 32 6 64

Solution /* a program to display the output as it appears on the right*/ #include<stdio.h> int main (void) {int i=0, product=1; while (i <=6) {printf("%i %i\n", i, product); product*=2; i++;} return(0);}

Example (While Statement) /* a program that displays the multiple of 5 from 0 to 20 */ #include<stdio.h> int main(void) {int mult; mult=5; while (mult<=20) {printf("%i\n", mult); mult+=5;} return(0);}