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לולאות

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Department of Computer Science-BGU

מבנה הלולאה

?

?

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(loop )לולאה

Used to repeat the same instruction(s) over and over again.

C provides some flexible ways of deciding how many times to loop, or when to exit a loop.

for, while, do-while loops.

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While

while (condition) {statement(s);

}

The statements are executed as long

as condition is true

When the condition is no

longer true, the loop is exited.

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factorial דוגמא-

#include <stdio.h>void main() {

int i, n, fact = 1;printf("Enter a number\n");scanf("%d", &n);i=1; while (i<=n) {

fact = fact*i;i++;

}printf("the factorial is %d\n", fact);

}

This is a counter

Every iteration i is incremented by 1.

(Equivalent to i=i+1)

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Exercise

Input – Two integers – A and B

Output – How many times A contains B This is the result of the integer division

A/BNote –

Do not use the division operator!

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Solution


int a, b, res;

printf("Please enter two numbers.\n");scanf("%d%d", &a, &b);

res = 0;while ( (res+1) * b <= a)

res = res + 1;

printf("%d / %d = %d", a, b, res);}

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Additional Exercise

Input – Two integers – A and B

Output – Only if A and B are Digits Otherwise return to input.

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Solution


int a, b, flag = 1;while ( flag){

flag = 0;printf("Please enter two numbers.\n");scanf("%d%d", &a, &b);if(a > 9 || a < 0)

flag = 1;else if (b > 9 || b < 0 )

flag = 1;}

// executing statements using a and b}

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Compact Solution


int a, b, flag = 1;while ( flag){

flag = 0;printf("Please enter two numbers.\n");scanf("%d%d", &a, &b);if(a > 9 || a < 0 || b > 9 || b < 0 )

flag = 1;}

// executing statements using a and b

}19/04/23 00:22

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do - while לולאה

do {statement(s)

} while (expression);

Similar to while loops Except the condition is evaluated after the loop

body The loop body is always executed at least once,

even if the expression is never true (equals zero)

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לקלוט נתון לפי הדרישה


int i;printf("Please enter a positive number.\n");do { scanf("%d", &i);

if (i<=0) printf("That's not a positive number! Try again.\n");} while (i<=0);

/* The program continues.... */}

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- מבנה forלולאה

/* Program before the for loop */

for( ; ; ) {

loop body;} /* Continue the program after for loop */

initiali ze

condition increment

True

False

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דוגמא

For loops are controlled by a counter variable.

for( c =init_value; c<=fin_value ; c+=increment_value)

{loop body;

}

c is a counter.

c is a incremented after every iteration

(can also be decreased!)

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for vs . while

for is equivalent to while… Any for loop can be converted to while loop and vice versa.

If we want to perform something for a predefined number of times, better use for.

If we just wait for something to happen (not after a certain number or iterations), better use while.

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break

When break is encountered, the loop is exited regardless of whether the condition is still true.

The program then continues to run from the first line after the while loop.

If called within a nested loop, break breaks out of the inner loop only.

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breakשימושים ב-

void main () {..

loop(expression) {..

break;..

}

// continue with the program

}

void main () { . loop1(expression1) {

. loop2(expression2) {

.

break;.

} // end loop2

// continue with loop1 } // end loop1

.

.}

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breakלקלוט נתון לפי הדרישה עם


int i;printf("Please enter a positive number.\n");do { scanf("%d", &i);

if (i >= 0) break; // after break no needed else printf("That's not a positive number! Try again.\n");} while (1);

/* The program continues.... */}

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continue

When continue is encountered, the rest of the loop is ignored.

The program then continues to run from the beginning of the loop.

Rarely used.Can usually be replaced by an

appropriate if-else statement.

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continueשימוש ב-

void main () {..

loop(expression) {..

continue;..

}

// continue with the program}

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תרגיל פשוט

כתוב תכנית שמדפיסה את טבלת הכפל:פתרון#include <stdio.h >

void main(){ int i,j;

printf("Printing the multiplication table: \n\r"); for (i = 1 ; i <= 4 ; i++) { printf("\n\r"); for (j = 1 ; j <= 5 ; j++) printf ("(%2d , %2d)", i, j); }

}19/04/23 00:22Department of Computer Science-BGU

תרגיל

Write a program that accepts a number from the user,

and checks whether it is prime.

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פתרון

#include >stdio.h>void main() {

int i, num;printf("enter a number\n");scanf("%d", &num);for(i = 2 ; i > num; i++)

if (num % i == 0) /* Then we know it's not a prime */break;

if (i > num) printf("%d is not a prime number!\n", num);

elseprintf("%d is indeed a prime number!\n", num);

}

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תרגיל נוסף

Extend the former program so it accepts a number from the user,

and prints out all of the prime numbers up to that number

(Hint – gotta use nested loops here...)

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פתרון


int i, j, last;printf("enter a number\n");scanf("%d", &last);for(i = 2; i >= last; i++) {

for(j = 2 ; j > i; j++)if (i % j == 0)

break;if (j == i)

printf("the number %d is prime\n", i); } // end for

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תרגיל נוסף

Write a program that prints an upside-down half triangle of.*

The height of the pyramid is the input.

***************

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הנה הפתרון

#include>stdio.h>

void main() {int i, j, size;

printf(“Please enter a size:\n”);scanf(“%d”,&size);for (i = 1; i >= size; i++) {

for(j = i; j >= size; j++)printf("*");

printf("\n");}

}

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שינוי בתרגיל

Change the former prime-listing program ,

so that is displays only the largest prime number

which is smaller than or equal to the user’s input.

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1פתרון


int i, j, last;int found = 0; /* This indicates whether we found the largest prime */printf("enter a number\n");scanf("%d", &last);i = last;while (!found) { /* Loop until we find our guy */

for(j = 2 ; j > i; j++) if (i % j == 0) break;if (j == i) /* If this is true then i is prime */ found = 1; else i--;

}printf("The largest prime not larger than %d is %d.\n", last, i);

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break – עם 2פתרון


int i, j, last;printf("enter a number\n");scanf("%d", &last);for(i=last ; i>1 ; i--) {

for(j = 2 ; j < i; j++) if (i % j == 0) break; // break the inner for loop

only !!if (j == i) // i is prime. We found our guy break;

}printf("The largest prime not larger than %d is %d.\n", last, i);

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