Direct Computation for Exercise 2-1

[ChenZhongPu]

types_ranges.c relies on limits.h. Here is the direct computation way as indicated in the book.

#include <stdio.h>

/**
 * K&R Exercise 2-1: Write a program to determine the ranges of char, short,
 * int, and long variables, both signed and unsigned, by direct computation.
 *
 * This method calculates the ranges by understanding their bitwise representation
 * (specifically two's complement for signed types).
 */

int main() {
    printf("--- Data Type Ranges by Direct Computation ---\n\n");

    // --- Character Types ---
    // For any unsigned type, a bit pattern of all 1s (~0) is the maximum value.
    unsigned char uchar_max = ~0;
    // For a signed type, the max value has the sign bit as 0 and all other bits as 1.
    // This can be calculated by shifting the unsigned max right by one.
    signed char schar_max = uchar_max >> 1;
    // In two's complement, the minimum value is the bitwise NOT of the max value.
    signed char schar_min = ~schar_max;
    printf("Signed Char:   %d to %d\n", schar_min, schar_max);
    printf("Unsigned Char: 0 to %u\n\n", uchar_max);

    // --- Short Types ---
    unsigned short ushort_max = ~0;
    signed short sshort_max = ushort_max >> 1;
    signed short sshort_min = ~sshort_max;
    printf("Signed Short:  %d to %d\n", sshort_min, sshort_max);
    printf("Unsigned Short: 0 to %u\n\n", ushort_max);

    // --- Int Types ---
    unsigned int uint_max = ~0;
    signed int sint_max = uint_max >> 1;
    signed int sint_min = ~sint_max;
    printf("Signed Int:    %d to %d\n", sint_min, sint_max);
    printf("Unsigned Int:  0 to %u\n\n", uint_max);

    // --- Long Types ---
    unsigned long ulong_max = ~0;
    signed long slong_max = ulong_max >> 1;
    signed long slong_min = ~slong_max;
    printf("Signed Long:   %ld to %ld\n", slong_min, slong_max);
    printf("Unsigned Long: 0 to %lu\n\n", ulong_max);

    // --- Long Long Types (from C99 standard) ---
    unsigned long long ullong_max = ~0;
    signed long long sllong_max = ullong_max >> 1;
    signed long long sllong_min = ~sllong_max;
    printf("Signed Long Long:   %lld to %lld\n", sllong_min, sllong_max);
    printf("Unsigned Long Long: 0 to %llu\n\n", ullong_max);

    return 0;
}

[berkenvr]

Since this question is before the bitwise topic, I think it is not appropriate to use bitwise in the answer

[ChenZhongPu]

The version without bitwise operations:

    unsigned char uchar_max = -1;  // -1 wraps around to max value for unsigned
    signed char schar_max = (unsigned char)(-1) / 2;  // Half of unsigned max
    signed char schar_min = -schar_max - 1;  // One less than negative of max