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variables values not showing equal

Dnyaneshwar07

Hello everyone,

                       i am using renesas rx231 series microcontroller and E2 studio ide for code development,

                         i have written one small code in which i have taken one signed int whoes value is -3871,and another variable which is also same signed int with value of 61665 which its 2's compliment value  -3871and another same variable i have taken signed int with hex value of -3871 which is 0xF0E1 ,with this i have written one if else statement but it is not working/not showing the same value.

signed int i = -3871;
signed int j = 0xf0e1;
signed int k = 61165;

_Bool m;

void main(void)
{

while(1)
{
R_Config_WDT_Restart();

if(j == k)
{
m = 1;
}
else if(j == i)
{
m = 1;
}
else if(k == i)
{
m = 1;
}
else
{
m = 0;
}
}

}

value of m remains 0 always.why this is happening??

please any can explain this?

  • Are you sure that the data type int is 2 bytes and not 4 bytes?

    You are using only 2 bytes (16 bits) to represent an int value. It is more common to use 4 bytes (32 bits). I don't know the compiler you are using.

  • In situations like this, there are lots of things you can do to better understand what the compiler is doing. One way is to examine the assembler listing file (enable it in your project settings in whatever IDE you're using). Another way is to manually observe from your debugger tool's memory or variable dump. Yet another way is to write yourself a print function which will dump memory (you can cast the pointer to your variables to say char type) and then sequentially dump out each memory location for your variables so you can inspect them. Also, get used to examining the settings in the IDE for the project, because some compilers can be configured for different data sizes. Also, check the optimisation settings, just in case if you're not actually using a variable (you are not using the variable m at all, you are only setting it) the compiler may remove it completely, i.e. optimise it out, because you don't specify how you checked m. Also, you could consider making use of stdint.h (uint8_t etc).

  • ints are typically 4 bytes or -2,147,483,648 to 2,147,483,647 therefore an unsigned int are 0 to 4,294,967,295,  or an int8 is only -128 to 127.  Your processor supports 8, 16, 32-bit ints. you have to know which one you are using..  

  • Former Member
    Former Member

    Your MCU is a 32-bit machine.  So, this should be similar to the x386 or 32-bit RPi integer size which is 32 bits.  I'd guess that your C-compiler goes along with that.

    Why the above loop?  I don't belive that i, j, and k ever change value. 

    Anyhow, on my RPi2 (32 bits), I get i = -3871,  j = 61665,  k = 61165 i.e. m = 0.

  • You would do yourself a favour by using more modern C coding practice:

    add these includes to the start of every module:

    #include <stdint.h>
    #include <stdbool.h>

    declare 16 bit integers like this:

    uint16_t auto_zero_pw = 12345;

    int16_t temperature = -10;

    and Booleans like this:

    bool alarm_flag = false;

    This way you will know  how many bits your variables are.

    You should never set a bool to values other than true or false and you should never test it against values other than true or false.

    It sounds pedantic but it helps to reduce errors.

    MK

  •  with your variables and as already stated, your probably working with 32bit ints

    i= oxFFFFF0E1

    j=0x0000F0E1

    k=0x0000F0E1

    So you will always get m=0

    Specifying the int16 should fix this.

    adding some debug statements inside each else block to print the result of the comparison will confirm the error. or simply change the m= statements to an int and assign different values to each compare. Obviously this is test code and your figuring things out so i hope this helps.

  • All those 32 bit examples show j = k = 61665.

    Shouldn't m still be 1, as the first if statement is true?

     - W.Thinking

    edit: equal sign.

  • Former Member
    Former Member in reply to wolfgangfriedrich

    signed int i = -3871;
    signed int j = 0xf0e1; # j = 61665 != k = 61165
    signed int k = 61165;