Problem while defining conditions for multiple variables in C - c

Question

I'm trying to write a program in C that receives three integers and uses This Method
But I only want the inputs to be in the range of 1-100 (including 1 and 100)
#include <stdio.h>
int main(){
int a , b , c = 50;
do{
scanf("%d %d %d", &a, &b, &c);
}
while((a > 100 || a < 1)&& (b > 100 || b < 1) && (c > 100 || c < 1));
if (a+b > c && a+c>b && b+c>a){
printf("%d\n", a+b+c);
}
else {
printf("invalid\n");
}
And it somehow doesn't consider the conditions
for example if I enter something like 1000 -5 4 It won't reprompt me for a new input
But the weird thing is that if i only consider one of the conditions it will work fine with that one variable! for example if i put something like while((a > 100 || a < 1); in there, it will then reject an input like 1000 2 4
How do I make it that it considers the conditions for all the variables?
Any help would be appreciated!

Answer 1

To check for any of the variable for range, change
while((a > 100 || a < 1)&& (b > 100 || b < 1) && (c > 100 || c < 1));
^^
// Will produce a FALSE value if 'a' is within expected range, and due to
// short-circuit, it'll not evaluate other conditions.
to
while((a > 100 || a < 1) || (b > 100 || b < 1) || (c > 100 || c < 1));
That said, couple of other points:
int a , b , c = 50; only initializes c, other variables are uninitialised and contain indeterminate values. Be a little more explicit, declare and define each variable in separate line (not a technical requirement, sake of readability and maintainability while being technically correct).
Always check for the success of scanf(), before using the scanned values. Better, do away with scanf() for user inputs and use fgets() instead.

Answer 2

more readable :
while(!( 1 <= a && a <= 100 && 1 <= b && b <= 100 && 1 <= c && c <= 100));

Answer 3

Your loop will only continue if all three of a, b, and c are out of range - in your example of 1000 -5 4, the condition (c > 100 || c < 1) evaluates to false (0), so the whole expression evaluates to false and the loop exits.
You need to change the sense of the test, such that it will continue if any of a, b, or c are out of range. There are a couple of ways to do this:
while ( (a < 1 || a > 100) || (b < 1 || b > 100) || (c < 1 || c > 100) );
Changing the && to || means that the expression will evaluate to true and the loop will continue if any one of a, b, or c are out of range.
Another option:
while ( !(1 <= a && a <= 100) && (1 <= b && b <= 100) && (1 <= c && c <= 100 ) );
This will cause the loop to exit if all three of a, b, and c are in range.
You should also check the result of scanf to make sure you read all 3 inputs:
do
{
if ( scanf ( "%d %d %d", &a, &b, &c ) != 3 ) )
{
if ( feof( stdin ) || ferror( stdin ) )
{
fputs( "Error or EOF on input, exiting", stderr );
return EXIT_FAILURE;
}
else
{
fputs( "Bad input detected, clearing input stream", stderr );
/**
* Read and discard everything up to the next newline character
*/
while ( getchar() != '\n' )
; // empty loop
/**
* Unconditionally branch back to the beginning of the loop since
* at least one of a, b, and c wasn't read at all (i.e., don't
* rely on the test since what you're testing isn't valid).
*/
continue;
}
}
} while ( (a < 1 || a > 100) || (b < 1 || b > 100) || (c < 1 || c > 100 ) );