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While loop, do-while loop and for

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Join Date: Feb 2009

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chriscross86 chriscross86 is offline

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While loop, do-while loop and for

Feb 20th, 2009

hi,
there...ive come up with these codes and they work.but i dont know how to modify the program so that it prints sequence of asterisks in a single line based on the input gained using :
1.while
2.do-while
3.for

please help...

#include <stdio.h>

int main()

{

int x;

printf("Enter an integer\n");
scanf("%d", &x);

if((x<=20)&&(x>0))
{

}

else
{
printf("You have entered an invalid integer.Please enter a number smaller or equals to 20");

}

while((x>20)||(x<=0)){
printf("\nEnter a valid integer \n");
scanf("%d",&x);

}
printf("valid");
return 0;

}

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Join Date: Mar 2008

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William Hemsworth William Hemsworth is offline

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Nearly a Posting Virtuoso

Re: While loop, do-while loop and for

Feb 20th, 2009

In future, remember to use code tags.

Here is the code how I would have formatted it, after cleaning it up a little for you.

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
#include <stdio.h>
 
int main() {
  int x;
 
  printf("Enter an integer:\n");
  scanf("%d", &x);
 
  if ( !((x <= 20) && (x > 0)) ) {
    printf("\nYou have entered an invalid integer.\nPlease enter a number smaller or equal to 20:\n");
  }
 
  while ( (x > 20) || (x <= 0) ){
    printf("\nEnter a valid integer:\n");
    scanf("%d",&x);
  }
 
  printf("\nvalid");
 
  return 0;
}
#include <stdio.h>

int main() {
  int x;

  printf("Enter an integer:\n");
  scanf("%d", &x);

  if ( !((x <= 20) && (x > 0)) ) {
    printf("\nYou have entered an invalid integer.\nPlease enter a number smaller or equal to 20:\n");
  }

  while ( (x > 20) || (x <= 0) ){
    printf("\nEnter a valid integer:\n");
    scanf("%d",&x);
  }

  printf("\nvalid");

  return 0;
}

•

prints sequence of asterisks in a single line based on the input gained using :
1.while
2.do-while
3.for

First, all three of these will do a very similar thing (loop until a condition is met), so the code for each will look quite similar.

So, if I understood correctly, you want to make a loop which will print as many asterisks' as the user inputs.

while:
Help with Code Tags

C Syntax (Toggle Plain Text)
```
while ( x-- != 0 ) {
  printf("*");
}
```
while ( x-- != 0 ) { printf("*"); }
This will keep decrementing x and displaying one asterisks at a time, until x == 0.
do-while:
Help with Code Tags

C Syntax (Toggle Plain Text)
```
do {
  printf("*");
} while ( --x != 0 );
```
do { printf("*"); } while ( --x != 0 );
Same applies for this one, but as the order in which the code executes has been changed, you have to decrement x before comparing it with 0 (by changing it to --x instead of x--).
for:
Help with Code Tags

C Syntax (Toggle Plain Text)
```
for (; x != 0; --x) {
  printf("*");
}
```
for (; x != 0; --x) { printf("*"); }
Once again, the same thing is happening, except the code looks a little different...

Hope this helps.

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Join Date: Dec 2008

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Dewey1040

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Re: While loop, do-while loop and for

Feb 20th, 2009

idk if its the same for everybody, but my teacher takes points off unless we use i, j, or k for loops. so you could do

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
do{
printf("\nEnter valid integer less than 20: ");
scanf("%d", &x);
}while(x > 0 && x <= 20);
 
for(i = 0; i < x; i++){
printf("*");
}
do{
printf("\nEnter valid integer less than 20: ");
scanf("%d", &x);
}while(x > 0 && x <= 20);

for(i = 0; i < x; i++){
printf("*");
}

etc...

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niek_e

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Re: While loop, do-while loop and for

Feb 20th, 2009

•

Originally Posted by Dewey1040

idk if its the same for everybody, but my teacher takes points off unless we use i, j, or k for loops.

For real? I agree that 'i,j,k' are quite commonly used as vars for a loop, but I can think of countless examples where i,j or k would be a very bad choice.
I personally only use 1-character-variables (such as i,j,k) if the loop is very short (no more then 3-4 lines). And I try to never use the same name twice in a program. That's to keep the code more readable.

I think your teacher is probably just a lazy guy and wants his students to use these names so that he can easily identify the loops in a code or something...

Last edited by niek_e; Feb 20th, 2009 at 9:55 am.

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William Hemsworth William Hemsworth is offline

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Re: While loop, do-while loop and for

Feb 20th, 2009

True, what about if you're making a graph... and need to plot some x & y coordinates, what would be more readable?

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
for (int i = 0; i < 10; ++i) {
  for (int j = 0; j < 10; ++j) {
    graph.plot(i, j);
  }
}
for (int i = 0; i < 10; ++i) {
  for (int j = 0; j < 10; ++j) {
    graph.plot(i, j);
  }
}

or...

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
for (int x = 0; x < 10; ++x) {
  for (int y = 0; y < 10; ++y) {
    graph.plot(x, y);
  }
}
for (int x = 0; x < 10; ++x) {
  for (int y = 0; y < 10; ++y) {
    graph.plot(x, y);
  }
}

Just use what seems appropriate, and don't stick with i, j, k just because they are more commonly used.

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Aia

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Re: While loop, do-while loop and for

Feb 20th, 2009

>True, what about if you're making a graph... and need to plot some x & y coordinates, what would be more readable?

Since we are splitting hair, let's declare those int variables outside those for loops. Portability to the lowest common denominator should be a concern.

Last edited by Aia; Feb 20th, 2009 at 10:50 am.

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Join Date: Mar 2008

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William Hemsworth William Hemsworth is offline

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Re: While loop, do-while loop and for

Feb 20th, 2009

•

Since we are splitting hair, let's declare those int variables outside those for loops. Portability to the lowest common denominator should be a concern.

Switching between the C and C++ forum can be so confusing sometimes

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nucleon

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Re: While loop, do-while loop and for

Feb 20th, 2009

Splitting hairs somewhat further, a better formatting for the printf with the long string is:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
    printf("\nYou have entered an invalid integer.\n"
           "Please enter a number smaller or equal to 20:\n");
    printf("\nYou have entered an invalid integer.\n"
           "Please enter a number smaller or equal to 20:\n");

String literals separated only by whitespace are concatenated by the compiler. A useful fact.

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Dewey1040

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Re: While loop, do-while loop and for

Feb 20th, 2009

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Originally Posted by niek_e

I think your teacher is probably just a lazy guy and wants his students to use these names so that he can easily identify the loops in a code or something...

lol i think its the exact opposite of that actually. i think hees such a perfectionist that he just has to give us rules like that to make us learn more things... same reason he makes us learn the exact titles of every chapter, section of the chapter, and every sub-section of the chapter.

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death_oclock death_oclock is offline

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Re: While loop, do-while loop and for

#10

Feb 21st, 2009

I hope that you at least recognize the importance of the programming concepts rather than memorizing the text of the book, like your neurotic teacher seems to think.