17.1.2001sudeshna sarkar, iit kharagpur 1 programming and data structure sudeshna sarkar lecture 7

17.1.2001 Sudeshna Sarkar, IIT Kharagpur1

Programming and Data Structure

Sudeshna Sarkar

Lecture 7


main (){

int sum=0;int input, inner, outer;

printf(“Input an integer : “);scanf (“%d”, &input) ;

for (outer=1; outer <= input; outer++) for (inner=0; inner < outer; inner++) sum += inner; printf (“The result is %d\n”, sum) ;

}


Some Loop Pitfalls

while (sum <= NUM) ;

sum = sum+2;for (i=0; i<=NUM; i++); sum = sum+i;

for (i=1; i!=10; i=i+2) sum = sum+i;

double x;for (x=0.0; x<10.0; x=x+0.2) printf(“%.18f”, x);


Doubles and floatsWhat you expect:0.0000000000000000000.2000000000000000000.400000000000000000.. .. ..9.0000000000000000009.2000000000000000009.4000000000000000009.6000000000000000009.800000000000000000

What you may get:

0.000000000000000000

0.200000000000000000

0.400000000000000000

.. .. ..

8.999999999999999999

9.199999999999999999

9.399999999999999999

9.59999999999999999

9.799999999999999999


Use ints as loop counters

int i;

double x;

for (i=0; i<50; i=i+1)

{

x = (double)i/5.0;

printf (“%.18f”, x);

}


Iteration Summary

General Pattern : initialize test do stuff update go back to re-test, re-do stuff, re-update, ...

while and for are equally general in C use for when initialize/test/update are simple,

especially when counting.


Event Driven Programming

General Pattern : Program starts, sets itself up. Waits for some event or command to happen

mouse click, key click, timer, menu selection etc.

Program performs operation (“handles” the command)

Program goes back to waiting.


Simple Command Interpreter Read in “commands” and execute them. Input - single characters

a - execute command Add by calling Add() s - execute command Sub by calling Sub() q - quit

Pseudocode for main loop: get next command if a, execute command Add() if b, execute command Sub() if q, signal quit


Command Interpreter Loop Control

repeat until quit signal

use variable “done” to indicate when done

set done to falsewhile not done body statements if quit command, set done to true


Command Interpreter program

#define FALSE 0

#define TRUE 1

int main (void)

{

char command;

int done = FALSE;

while (!done) {

printf (“Input command:”);

scanf(“%c”,&command);

switch (command) {

case ‘A’:

case ‘a’: Add();

break;

case ‘S’:

case ‘s’: Sub();

break;

case ‘Q’:

case ‘q’: done=TRUE;

}

}

}


Exercise a

Write a C program which accepts as input a single integer k, then writes a pattern consisting of a single 1 on the first line, two 2s on the 2nd line, three 3s on the 3rd line, until it writes k occurrences of k on the last line.For example, if the input is 4, the output should be:12 23 3 34 4 4 4


Exercise b

Write a C program which accepts as input a single integer k, then generates the following pattern of k lines:For example, if the input is 5, the output should be: 1 2 2 2 3 3 3 3 3 4 4 4 4 4 4 45 5 5 5 5 5 5 5 5


Test if a number is prime

prime = 1;

for (i=2; i<num; i++)

{

if (num%i == 0)

prime=0;

}

if (prime == 1)

printf (“%d” is a prime number\n”);


Test if a number is prime

prime = 1;

limit = sqrt ((double)num);

for (i=2; i<limit; i++)

{

if (num%i == 0) {

prime=0;

break;

}

}

if (prime == 1)

printf (“%d” is a prime number\n”);


Break and continue

These two statements are used in loop control “break” exits the innermost current loop (for,

while, do-while) and to exit from a switchControl will be transferred out of the loop

“continue” starts the next iteration of the loop (for, while, do-while)

used to bypass the remainder of the current pass through a loop


do {

scanf (“%f”, &x);

if (x<0) {

printf(“Error, neg x”);

break;

}

. . .

/*process non-neg x */

} while (x<=100);

for (count=0;count<n;count++)

{

. . .

while ((c=getchar()) != ‘\n’)

{

if (c==‘*’) break;

. . .

}

}


do {

scanf (“%f”, &x);

if (x<0) {

printf(“Neg value forx”);

continue;

}

. . .

/*process non-neg x */

} while (x<=100);


Ex: Write a loop that will calculate the sum of an AP series upto n terms

Sum= a + (a+d) +(a+2d) + . . . + (a+ (n-1)d)

sum = a;for (i=1; i<n; i++){ sum = sum +a+ i*d;}printf (‘%d”, sum);

sum = a; term = a;for (i=1; i<n; i++){ term = term + d; sum = sum + term;}printf (‘%d”, sum);


Exercise c

Write a C program that takes as input a positive integer n, and prints all prime numbers between 2 and n.


Exercise d

Write a C program that calculates the sum of the first n odd numbers:1 + 3 + 5 + . . . + 2*n-1


The sine of x can be calculated approximately by summin the first n terms of the infinite series: sin x = x - x3 /3! + x5 /5! – x7 /7! + . . .

where x is expressed in radians ( radians = 180 degrees).

Write a C program that will read in a value for x and will calculate its sine.

(i) sum the first n terms (ii)continue adding successive terms till the value of

the next term becomes smaller (in magnitude) than 10-5


scanf (“%f”, &x);x = x*PI/180.0;sineval = x; term = x;for (i=1; i<n; i++){ term = (-1)*term*x*x/(2*i*(2*i+1)); sineval = sineval + term;}


scanf (“%f”, &x);x = x*PI/180.0;sineval = x; term = x;for (i=1; term<0.00001; i++){ term = (-1)*term*x*x/(2*i*(2*i+1)); sineval = sineval + term;}printf (“The value of sine is %f to %d terms\n”,sineval, i);

17.1.2001sudeshna sarkar, iit kharagpur 1 programming and data structure sudeshna sarkar lecture 7

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