1. Week 3 – Repetition (ctd.)
While, Do-While, For statements

2. Repetition: Looping
Allows execution of statement or block of statements more than once
Often used in programs to validate inputs or to process (transform) inputs
In C programming language, can use While, Do-While, For statements
A single statement or block of statements contained within {} can be repeatedly executed

3. While Statement (Pre-test Loop)
Often want to test the condition before even executing a loop the first time
For this use a While or For statement is appropriate; if you don’t know how many times code is to be repeated use a While statement
While statement syntax:
while (condition)
stmt; /* statement is executed as long as condition is true (i.e. until condition is false) */

4. While Statement Example
main()
{ int numstudents, mark, numread = 0;
int total = 0;
double avg;
printf("Enter number of students: ");
scanf("%d", &numstudents);
while (numread < numstudents)
{ printf("Enter mark:");
scanf ("%d", &mark);
total = total + mark;
numread = numread + 1; }
avg = total / numstudents;
printf("Average of %d students is: %.2lf\n",numstudents,avg);

5. For Statement
Used if we know how many times a block of code is to be repeated; for example if we want to calculate an average for each student in a class of 10 students we want to repeat it 10 times
For statement syntax:
for (execute once before entering loop; condition; execute before evaluating condition)
stmt;

6. For Statement Example main() { int i, mark, total = 0; double avg;
for (i = 1; i <= 5; i = i+1)
{ printf("Enter mark %d:",i);
scanf ("%d", &mark);
total = total + mark; }
avg = total / 5;
printf("Average of 5 students is: %.2lf\n",avg);

7. Do-While Statement (Post-test Loop)
Often want to execute the statement(s) before testing the condition, even for the first time; i.e. the block of code in the do-while loop is always executed unconditionally the first time
Often used for validating input
Do - While statement syntax: do
stmt;
while (condition) /* statement is executed as long as condition is true (i.e. until condition is false) */

8. Do - While Statement Example
main()
{ int numstudents = 0; do
{ if (numstudents < 0)
printf("Invalid! Number must be >= 0\n");
printf("Enter number of students: ");
scanf("%d", &numstudents);
} while (numstudents < 0);
printf("Number of students in class: %d\n", numstudents); }