Addition of two numbers in c

Question

Is there any possibilities to read and add two or three different integers by using single variable ( int a ) in C language?

I didn't want to use array

This question ia asked to me when I am attended the programming competition in my college — Vasanth Kumar, Oct 09 '15 at 12:14
sounds funny kind of... are you reading this input from an input stream or you have the values figured out already? — Kevin Constantine, Oct 09 '15 at 12:16
Seriously, if you want to add 4 8bit integer with a single 32bit integer, or 2 16bit integers with a single 32bit integer, you can use pointer casting and bitshift to do that — LPs, Oct 09 '15 at 12:16
@LPs I am curious to know, How it is possible with single variable ? Can you explain with example ? — Mohan, Oct 09 '15 at 12:26
Or you `malloc` a struct to a single pointer which contains all data. Also just a single variable. Heck, who makes such constraints? A PIC12 programmer? — too honest for this site, Oct 09 '15 at 13:31

score 3 · Answer 1 · edited May 23 '17 at 11:58

3

I'm not sure I'm getting you, but for example, if you want to add 2 16 bits integers with a single 32bit integer, you could do

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

int main()
{
    uint32_t a;

    printf("Enter number 1: ");
    scanf("%hd", (uint16_t *)(&a));

    printf("Enter number 2: ");
    scanf("%hd", ((uint16_t *)(&a))+1);

    printf("%X\n", a);

    printf("Sum = %"PRIu32"\n", (uint32_t)(*(uint16_t *)(&a)) + *(((uint16_t *)(&a)) + 1));

    return 0;
}

The logic is to think about variable equals to arrays of bytes, and that's it.

This implementation still have problems that are well explained HERE

edited May 23 '17 at 11:58

Community

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answered Oct 09 '15 at 12:26

LPs

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Violating strict aliasing rule and depends on endianess. – too honest for this site Oct 09 '15 at 12:33
@Olaf ...but it works. – LPs Oct 09 '15 at 12:35
@Olaf Edited and splitted. The avenger changes the DV – LPs Oct 09 '15 at 12:38
1

There is no DV! Please just add a note about the problems. "It works" is too often said about UB before the rocket explodes. – too honest for this site Oct 09 '15 at 12:41
@LPs you are missing something in last line... printf("Sum = %d\n", (uint32_t)(*(uint16_t *)(&a)) + *(((uint16_t *)(&a)) + 1)); – Mohan Oct 09 '15 at 12:57
@Mohan Yes, you right. Thx. I edited. – LPs Oct 09 '15 at 13:03
After @Mohans comment: You use the wrong format specifier (for `signed int`), even **iff** `uint32_t` was `unsigned int`. For `stdint.h` use `inttypes.h` format macros, here that would be `PRIu32`. – too honest for this site Oct 09 '15 at 13:05
@Olaf Good multi-platform catch. I edited. – LPs Oct 09 '15 at 13:22
@Olaf I now realize you wrote there is a problem with endianess. Where and why? – LPs Oct 10 '15 at 07:07
@LPs: Sorry, that was a mistake. You just use the uint32_t like an `uint16_t[2]` and do not shift. Anyway, that is a stupid constraint: forcing standard violation for - what? For not saving any memory & being less readable. Who makes such constraints? (this is a rhetorical questions, I well know there are enough id*ts in the word) – too honest for this site Oct 10 '15 at 11:49

score 0 · Answer 2 · answered Oct 09 '15 at 12:12

0

No. Every time you you atribute a new value to the same variable it replaces the old one. If you don't want to use an array and it's a simple code to add numbers, just declare three variables and atribute each value to one of them.

answered Oct 09 '15 at 12:12

Rafael Carneiro de Moraes

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Actually two variables are sufficient. – too honest for this site Oct 09 '15 at 14:00
He said two or three, so... – Rafael Carneiro de Moraes Oct 09 '15 at 16:23
"... add two or three different integer (**values**) by using single **variable**" (bold addition mine) – too honest for this site Oct 09 '15 at 16:58

score 0 · Answer 3 · answered Oct 09 '15 at 12:40

0

I do not know if you would like this, but another way you can do this will be to accept inputs like you punch in calculators, and parse to int before applying the operations on them.

Something like this

#include <stdio.h>
#include <string.h>

int main ()
{
    char buffer[256];
    char * pch;

    printf("input your numbers in this format ${number1}+${number2}...: ");
    fgets (buffer, 256, stdin);

    int sum = 0;
    pch = strtok (buffer, "+");
    while (pch != NULL)
    {
        sum += atoi (pch);
        pch = strtok (NULL, "+");
    }
    printf("the sum is %\n", sum);
    return 0;
}

so, run it and input 2+2+2 and it does the calculation for you. thanks

answered Oct 09 '15 at 12:40

Kevin Constantine

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There are too many variables in your code! – too honest for this site Oct 09 '15 at 13:30
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@Olaf that wasn't the problem... the problem was how to sum sets of inputs of number using one int variable instead of using array. – Kevin Constantine Oct 09 '15 at 13:36
The question as given states different. If you have more information than given here, you should include in your answer. – too honest for this site Oct 09 '15 at 13:41
@Olaf I considered conditions where the user might want more than 3 number inputs, let's say 20. how would you solve it using the approach of the first answer? that was what i got into consideration before doing this. and i stated clearly, that this might be another approach – Kevin Constantine Oct 09 '15 at 13:46

Addition of two numbers in c

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