CP104 Introduction to Programming Repetition and loop Lecture 13 __ 1

Do-while loop

• Syntaxdo statementwhile (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?

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 2

Case study: convert a decimal integer to binary

• Get an

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 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);}

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 4

For loop syntax

• Syntax of for loopfor (expression 1; expression 2; expression 3)statement

• Example for (i=1;i<=100;i++)

{sum += i;}

• Execution1. execute the expression 1

2. Execute expression 2. If true, then execute the statement. Then go to step 3. If false, go to step 4

3. Execute expression 3, then go to step 2

4. Leave the for loop, execute the statement following the for loop

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 5

Variations of for loop

1. 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++;}

2. for (i=1,j=100;i<=j; i++,j--) k = i+j;may have more than one variables

3. for (i=1; i<=100;i++,i++) sum +=i; for (i=1; i<=100;i=i+2) sum +=i;

4. for ( ; (c=getchar())!=’\n’;) printf(“%c”,c);

5. loop forever (infinite loop) for (;;) statement while (1) statement

for (i=1; ;i++) sum +=i; i=1; while(1){sum+=i; i++;}

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 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 = 3.1415*r*r; if (area>100) break; printf(“%f”, area);}

What does this for loop do?

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 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 = 3.1415*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); }

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 8

Example: test if a given integer is a prime

• Analysis1. input a positive integer m2. Output: m is prime if m is not divisible by any integer

between 2 and m-1; otherwise m is not prime

• Algorithm1. Get m2. k = sqrt(m), i = 23. For i from 2 to k

if i%m == 0; output: m is not prime, break

4. If i > m, output m is prime

Why is the algorithm correct ?

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 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);}

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 10

Nested loop with different combinations

1. while ( ){ … while () {…} }

2. do { … do {…} } while ();} while ();

3. for ( ; ; ){ … for (; ;) {…} }

4. while ( ){ … do {…} while (); }

5. for (; ;) { … while() {…} … }

6. do { … for (; ;) {…} } while ();

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 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;

}

}

}

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 12

Function to Compute Factorial

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

CP104 Introduction to Programming Repetition and loop Lecture 13 __ 13

Test the function with a driver

#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);}

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