exiting a while loop with a negative integer

问题

I want to exit a while() when the user enters a negative number of any size. What kind of condition would I need at the start of the loop to get the loop to exit when the user enters a negative number?

回答1:

Use an if condition to know the number is less than 0 or not. And if yes, just use break statement inside it, which will bring you out of the loop. Learn more about break statement from MSDN.

回答2:

Well, what is a negative number? It's a number (call it x) that is less than zero, or symbolically, x < 0. If x is less than zero, then this is true. If not, then it is false.

You can loop endlessly and break when this condition is met:

while (1) {
  if (x < 0) {
    break;
  }

  ...
}

But I prefer to just use the opposite of that condition in the while loop itself:

 while (x >= 0) {
   ...

While the condition is true, then the loop continues. When it is false (and your original condition is true, as these two are opposite), the loop breaks.

回答3:

int i = -1;
do
{
    i = magic_user_input();
    //simple enough? get a decent programming book to get the hang of loops
}
while(i > -1)

edit: sorry, my mistake: 'i' wasn't declared properly :) now it should be fine to use

回答4:

Do not define your variable as unsigned variable. As suggested in other answers use if statement and break with if statement.

example:

int main(void)
{
 int i;
 while(1){
 /*here write an statement to get and store value in i*/ 
  if(i<0)
  {
    break;
  }
 /*other statements*/
  return(0);
  }
 }

来源：https://stackoverflow.com/questions/7761525/exiting-a-while-loop-with-a-negative-integer

标签

numbers

while-loop