Reversing an array In place

Question

Okay so I\'ve tried to print and Array and then reverse is using another array But I\'m trying to create a For Loop that will take an array and reverse all of the elements i

Answer 1

If you are not interested in writing functions for any numeric type, try macros for this task. This code same working with any built-in numeric type: int, float, double.

It has not a support for strings, since any string is ending on the character the NULL character \0. More a controlled version my similar answer is here https://stackoverflow.com/a/42063309/6003870 and contains solution for reverse a string.

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A full code

#include 

// print items of an array by a format
#define PRINT_ARRAY(array, length, format) \
{ \
    putchar('['); \
    for (size_t i = 0; i < length; ++i) { \
        printf(format, array[i]); \
        if (i < length - 1) printf(", "); \
    } \
    puts("]"); \
}


// reverse an array in place
#define REVERSE_ARRAY(array, length, status) \
    if (length > 0) { \
        for (int i = 0; i < length / 2; ++i) { \
            double temp; \
            temp = array[i]; \
            array[i] = array[length - i - 1]; \
            array[length - i - 1] = temp; \
        } \
        *status = 0; \
    } \
    else if (length < 0) *status = -1; \
    else *status = 1;

#define SUCCESS_REVERSE_ARRAY_MSG "An array succefully reversed"
#define FAILED_REVERSE_ARRAY_MSG "Failed reverse for an array"
#define NO_CHANGED_REVERSE_ARRAY_MSG "An array no changed"


/*
    Print message about status reverse an array
 */
static void
print_msg_reverse_array_status(const int status)
{
    if (status == 0) printf("Status: %s\n", SUCCESS_REVERSE_ARRAY_MSG);
    else if (status == -1) printf("Status: %s\n", FAILED_REVERSE_ARRAY_MSG);
    else if (status == 1) printf("Status: %s\n", NO_CHANGED_REVERSE_ARRAY_MSG);
}


int
main (const int argc, const char *argv[])
{
    // keep value of status
    int status;

    puts("\tExample reverse of an integer array");
    int arr_int[5] = {1, 2, 3, 4, 5};

    status = 0;
    PRINT_ARRAY(arr_int, 5, "%d");
    REVERSE_ARRAY(arr_int, -1, &status);

    // will be an error, since a length is less 0, and the array is not changed
    print_msg_reverse_array_status(status);
    PRINT_ARRAY(arr_int, 5, "%d");

    status = 0;
    REVERSE_ARRAY(arr_int, 0, &status);

    // a length is equal to 0, so an array is not changed
    print_msg_reverse_array_status(status);
    PRINT_ARRAY(arr_int, 5, "%d");

    status = 0;
    REVERSE_ARRAY(arr_int, 5, &status);
    print_msg_reverse_array_status(status);
    PRINT_ARRAY(arr_int, 5, "%d");

    puts("\n\tExample reverse of an float array");
    float arr_float[5] = {0.78, 2.1, -3.1, 4, 5.012};

    status = 0;
    PRINT_ARRAY(arr_float, 5, "%5.3f");
    REVERSE_ARRAY(arr_float, 5, &status);
    print_msg_reverse_array_status(status);
    PRINT_ARRAY(arr_float, 5, "%5.3f");

    puts("\n\tExample reverse of an double array");
    double arr_double[5] = {0.00001, 20000.002, -3, 4, 5.29999999};

    status = 0;
    PRINT_ARRAY(arr_double, 5, "%8.5f");
    REVERSE_ARRAY(arr_double, 5, &status);
    print_msg_reverse_array_status(status);
    PRINT_ARRAY(arr_double, 5, "%8.5f");
    return 0;
}

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I am used the GCC for compilation and your result must be as next

    Example reverse of an integer array
[1, 2, 3, 4, 5]
Status: Failed reverse for an array
[1, 2, 3, 4, 5]
Status: An array no changed
[1, 2, 3, 4, 5]
Status: An array succefully reversed
[5, 4, 3, 2, 1]

    Example reverse of an float array
[0.780, 2.100, -3.100, 4.000, 5.012]
Status: An array succefully reversed
[5.012, 4.000, -3.100, 2.100, 0.780]

    Example reverse of an double array
[ 0.00001, 20000.00200, -3.00000,  4.00000,  5.30000]
Status: An array succefully reversed
[ 5.30000,  4.00000, -3.00000, 20000.00000,  0.00000]

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Testing environment

$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.6 (jessie)
Release:    8.6
Codename:   jessie
$ uname -a
Linux localhost 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64 GNU/Linux
$ gcc --version
gcc (Debian 4.9.2-10) 4.9.2