while loop and arithmetic operator

Question

int i = 5; 

while(i>5)

printf("%d",i);                

prints nothing.

int i = 5;

while ( 5<i<10 )
{
printf("%d",i);                      
i++;
}

prints 5

In both the cases shouldn't be the result "prints nothing" . Because 5 is not less than 5.

Answer 1

In C integer is used as a boolean: 0 is false, everything else is true. As @JonathanLeffler noted (see his comment below), in C99 and C11 there is a standard boolean datatype, but it also expands to integer constants (0 and 1). Link.

When you write an expression like 5 < i < 10, it is treated like (5 < i) < 10, where 5 < i is a boolean expression, which returns 0. So you get (0) < 10, which is true, that's why the loop's body is executed. In order to make the loop condition correct, you shoould use something like:

while (5 < i && i < 10)