So I need the user input for an int to be greater than 2.
printf("Number of triangles (must be greater than 2) = ");
fflush(stdin);
scanf("%d", &num_of_triangles);
while (num_of_triangles < 3) // ?how to check using scanf?
{
printf("Number of triangles (must be greater than 2) = ");
fflush(stdin);
scanf("%d", &num_of_triangles);
}
Is there any possibility to optimize this code regarding the repeating lines?
Instead of while, use do...while. That way, the loop will always run at least once.
num_of_triangles = 0;
do {
printf("Number of triangles (must be greater than 2) = ");
scanf("%d", &num_of_triangles);
while (getchar() != '\n'); // this flushes the input buffer
} while (num_of_triangles < 3);
Also, don't fflush(stdin), as that's undefined behavior.
EDIT:
It seems that Visual Studio allows fflush(stdin). From MSDN:
The fflush function flushes a stream. If the file associated with stream is open for output, fflush writes to that file the contents of the buffer associated with the stream. If the stream is open for input, fflush clears the contents of the buffer. fflush negates the effect of any prior call to ungetc against stream. Also, fflush(NULL) flushes all streams opened for output. The stream remains open after the call. fflush has no effect on an unbuffered stream.
In general however, this behavior shouldn't be depended on. Doing something more portable like the above code is preferable.
getchar() will pick up the first value you enter instead of scanf.
// fflush on input stream is an extension to the C standardfflush(stdin) is undefined behaviour, so you need to remove that entirely and substitute something else.
You should also check for the outputs of scanf, in case it fails.
If you want to improve readability, you can also move the scanf into your while loop directly, like this
while (scanf("%d",&num_of_triangles)==1 && num_of_triangles < 3)
You can write your code as this -
printf("Number of triangles (must be greater than 2) = ");
while (scanf("%d",&num_of_triangles)==1 && num_of_triangles < 3) //check return of scanf as well as number
{
printf("Number of triangles (must be greater than 2) = ");
}
Loop will iterate until scanf is successful and num_of_triangles is less than 3.
while(scanf("%d", &num_of_triangles) != 1 || num_of_triangles < 3) so that the error message is displayed on invalid input such as a character. You also need to clear the stdin in case of invalid input.
fflush(stdin)is undefined behaviour.