1. Do-while loop
Syntax do statement while (loop repetition condition)
It first execute the statement, then do the check. If the condition is satisfied, then it execute the statement again; otherwise jump out the loop
While loop first check the condition. If it is satisfied, then it execute the statement. Otherwise it jump out.
#include <stdio.h>
main(void) {
int sum = 0, i = 1; do
{ sum += i*i;
i++; } while(i<=100);
printf(“The sum is %d.”, sum); }
What does this program do?

2. Case study: convert a decimal integer to binary
Get an

3. for Loop Statement Example #include <stdio.h> main(void) {
int sum = 0; for (i=1;i<=100;i++)
{ sum += i; }
printf(“The sum is %d.”, sum); }

4. For loop syntax
Syntax of for loop for (expression 1; expression 2; expression 3) statement
Example for (i=1;i<=100;i++)
{sum += i;}
Execution
execute the expression 1
Execute expression 2. If true, then execute the statement. Then go to step 3. If false, go to step 4
Execute expression 3, then go to step 2
Leave the for loop, execute the statement following the for loop

5. Variations of for loop
for (i=1; i<=100;i++) sum +=i;  i=1; for (; i<=100;i++) sum +=i;  for (i=1; i<=100;) {sum +=i; i++;}  i=1; for (; i<=100;) {sum +=i; i++;}
for (i=1,j=100;i<=j; i++,j--) k = i+j; may have more than one variables
for (i=1; i<=100;i++,i++) sum +=i;  for (i=1; i<=100;i=i+2) sum +=i;
for ( ; (c=getchar())!=’\n’;) printf(“%c”,c);
loop forever (infinite loop) for (;;) statement  while (1) statement
for (i=1; ;i++) sum +=i;  i=1; while(1){sum+=i; i++;}

6. break statement
break can be used to jump out a loop (either while-loop, or for loop) for (i=1;i<=10;r++) { area = *r*r; if (area>100) break; printf(“%f”, area); } What does this for loop do?

7. continue statement
break can be used to jump out a loop (either while-loop, or for loop) for (i=1;i<=10;r++) { area = *r*r; if (area>100) break; printf(“%f”, area); } What does this for loop do?
Continue can be used to skip the current iteration Example: find out the integers between 100 and 200 which are not divisible by 3. main() { int n; for (n =100;n<=200;n++) { if (n%3 == 0) continue; printf(“%d ”, n); }

8. Example: test if a given integer is a prime
Analysis
input a positive integer m
Output: m is prime if m is not divisible by any integer between 2 and m-1; otherwise m is not prime
Algorithm
Get m
k = sqrt(m), i = 2
For i from 2 to k if i%m == 0; output: m is not prime, break
If i > m, output m is prime
Why is the algorithm correct ?

9. Prime tester #include <stdio.h> #include <math.h> main() {
int m,i = 0,k;
scanf("%d", &m);
k = sqrt((double) m);
for (i=2;i<=k;i++)
if (m%i == 0)
{printf("%d is not a prime", m); break;} }
if (i>=k)
printf("%d is a prime", m);

10. Nested loop with different combinations
4. while ( ) { … do {…} while (); }
5. for (; ;) { … while() {…} … }
6. do { … for (; ;) {…} } while ();
while ( ) { … while () {…} }
do { … do {…} } while (); } while ();
for ( ; ; ) { … for (; ;) {…} }

11. Case Study: Find all Prime Numbers Between 100 and 200
Specification: print the results in rows, 10 prime each row.
#include <stdio.h>
#include <math.h>
main()
{ int m,i,k,n=0;
for (m = 101; m<=1000; m+=2)
{ if (n%10 == 0)
printf("\n");
k =(int) sqrt(m);
for (i=2;i<=k;i++)
{ if (m%i == 0) break; }
if (i>=k+1) {
printf("%d ", m);
n = n+1; }

12. Function to Compute Factorial
Factorial of an integer n is defined to be n*(n-1)*(n-2)*….*2*1
Denoted by n!

13. Test the function with a driver
n n!
#include <stdio.h>
#include <math.h>
int factorial(int);
int main(){ /* a test driver for factorial function */
int i=0;
printf("n n!\n");
for (i = 0; i<20; i++) {
printf("%d %d\n", i, factorial(i)); }
fflush(stdin);
getchar();
return 0;
int factorial(int n)
int i, product; /* accumulator for product computation */
product = 1;
/* Computes the product n x (n-1) x (n-2) x ... x 2 x 1 */
for (i = n; i > 1; --i) {
product = product * i;
/* Returns function result */
return (product);
What happens here