Introduction to Computing Lecture 06: Repetition and Loop Statements (Part I) Assist.Prof.Dr. Nükhet ÖZBEK Ege University Department of Electrical & Electronics Engineering nukhet.ozbek@ege.edu.tr

Topics Repetition in programs while statement do while statement for statement

Repetition in programs So far, the statements in the program body executes only once However, sometimes it is necessary to repeat a process many times Repetition steps in a program is called a loop

Repetition

Repetition int a1,a2,a3, … a50, sum; scanf(“%d”,&a1); scanf(“%d”,&a2); sum = a1 + a2 + a3 + … + a50; This is not feasible!

Repetition int a, sum=0; scanf(“%d”,&a); sum = sum + a; … This is not feasible either!

The while statement Implements the repetition in an algorithm Repeatedly executes a block of statements Tests a condition (Boolean expression) at the start of each iteration Terminates when condition becomes false (zero)

Example: addnum.c Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addnum.c (cont) Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count Iteration Control Initialize Check condition Update

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { return 0; } Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; return 0; } Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count only the variables sum and count are initialized to 0

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); return 0; } . Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) } return 0; Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } return 0; Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count Same as: count = count + 1; Decrement: count --; Same as: sum = sum + nextNum; Others: -=, *=, /=, etc.

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Read in numbers, add them, and print their sum and average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addnum.c (cont) totalNumbers count nextNum sum ???? 0.0

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addnum.c (cont) totalNumbers count nextNum sum ???? 0.0 3

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addnum.c (cont) totalNumbers count nextNum sum ???? 0.0 3 4 1 4.0

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addnum.c (cont) totalNumbers count nextNum sum ???? 0.0 3 4 -1 1 4.0 2 3.0

Example: addnum.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count = 0, totalNumbers; scanf("%d", &totalNumbers); while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addnum.c (cont) totalNumbers count nextNum sum ???? 0.0 3 4 -1 6.2 1 4.0 2 3.0 3 9.2

Syntax for while statement while (loop repetition condition) statement; OR { statement1; statement2; … statementn; }

Common Mistakes in while -- “one liners” while (num < minimum) scanf(“%d”, &num); printf(“Number must be greater than %d.\n”, minimum); printf(“Please try again.\n”); while (num < minimum) { scanf(“%d”, &num); } printf(“Number must be greater than %d.\n”, minimum); printf(“Please try again.\n”);

Common Mistakes in while -- “one liners” (cont) while (num < minimum) scanf(“%d”, &num); printf(“Number must be greater than %d.\n”, minimum); printf(“Please try again.\n”); while (num < minimum) { scanf(“%d”, &num); printf(“Number must be greater than %d.\n”, minimum); printf(“Please try again.\n”); }

Common Mistakes in while -- extra semi-colon; while (num < minimum); { scanf(“%d”, &num); printf(“Number must be greater than %d.\n”, minimum); printf(“Please try again.\n”); } Marks the end of the while-block -- usual cause of infinite loops

Common Mistakes in while Loop control variable is not updated. “Infinite loop” while (count < totalNumbers) { scanf("%f", &nextNum); sum += nextNum; } while (count < totalNumbers) { scanf("%f", &nextNum); sum += nextNum; count++; }

do … while Implements a post-tested loop do { printf(“Main menu:\n”); printf(“1. Account balance.\n”); printf(“2. Withdraw cash.\n”); printf(“3. Transfer funds.\n\n”); printf(“9. Exit\n\n”); printf(“Please enter your choice: “); scanf(“%d”, &choice); /* Insert selection instructions here. */ } while ( choice != 9 );

do … while (cont) do { printf(“Main menu:\n”); printf(“1. Account balance.\n”); printf(“2. Withdraw cash.\n”); printf(“3. Transfer funds.\n\n”); printf(“9. Exit\n\n”); printf(“Please enter your choice: “); scanf(“%d”, &choice); /* Insert selection instructions here. */ } while ( choice != 9 );

Syntax for do … while statement { statement1; statement2; … statementn; } while (loop repetition condition);

Notes on do … while do … while is executed at least one

The for statement Form of pre-tested loop which allows for initialization and iteration control Syntax: for (initialization; condition; update ) { instruction block } Careful! A semi-colon here marks the end of the instruction block!

Example: addfor.c Read in numbers, add them, and print the sum and the average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Example: addfor.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addfor.c (cont) Read in numbers, add them, and print the sum and the average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Initialize Example: addfor.c (cont) Read in numbers, add them, and #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Read in numbers, add them, and print the sum and the average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count Initialize

Check condition Example: addfor.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Read in numbers, add them, and print the sum and the average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count Check condition

The Update is performed AFTER the body of the loop #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addfor.c (cont) Read in numbers, add them, and print the sum and the average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count Update (aka Increment Step) IMPORTANT!! The Update is performed AFTER the body of the loop

Example: addfor.c (cont) #include <stdio.h> /**********************************\ Read in numbers and add them up Print out the sum and the average \**********************************/ int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n",sum/count); return 0; Example: addfor.c (cont) Read in numbers, add them, and print the sum and the average set sum to 0 set count to 0 input totalNumbers while (count < totalNumbers) { input nextNum add nextNum to sum add 1 to count } output "Sum was" sum output "Mean was" sum/count

Notes on for What is the value of x when the following statement is complete? for (x = 0; x < 100; x++) ; What is the value of ctr when the following statement is complete? for (ctr = 2; ctr < 10; ctr += 3) ;

Notes on for and while An equivalent for statement for a while statement can be written and vice versa

while and for #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); count = 0; while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0;

while and for (cont) Check condition Initialize #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); count = 0; while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; Check condition Initialize

while and for (cont) Check condition #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); count = 0; while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; Check condition

while and for (cont) Update #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); count = 0; while (count < totalNumbers) scanf("%f", &nextNum); sum += nextNum; count++; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; #include <stdio.h> int main() { float nextNum, sum = 0.0; int count, totalNumbers; scanf("%d", &totalNumbers); for ( count=0; count < totalNumbers; count++ ) scanf("%f", &nextNum); sum += nextNum; } printf("Sum was %f\n",sum); printf("Mean was %f\n", sum/count); return 0; Update