The while() loop is executing infinitely

I had a problem where have to print ASCII values of characters from 1 to 255 so I wrote this code:

#include<stdio.h>
int main()
{
     unsigned char a,z,A,Z;
     a=1;
    while (a<=255)
    {
        printf("the ascii value of %c is %d\n",a,a);
        a++;
    }
    return 0;
}

The code runs fine and prints the ASCII values till I think (a<=130) too but when I put the condition like while(a<=150) or while(a<=255)
it keeps executing infinitely. What may be the reason it is happening?

I was expecting that all the values will be printed.

>Solution :

Whether char is signed or unsigned on any given platform is implementation-defined. A signed char would overflow at a == 127, so a <= 150 can never become false.

a <= 255 can never become false regardless of the signedness of char. (Assuming 8-bit chars.)