I am trying to add two binary numbers in a c function, and I can't get the result I'm looking for.

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

char * sadd(char bn1[], char bn2[], char s[]){ //Function to add the binary numbers

        int i;
        int co = 0;
        int num = 0;

        for(i = 15; i>0; i  ){
                num = (int)bn1[i]   (int)bn2[i]   co;
                co = 0;
                if(num == 2){
                        co = 1;
                        s[i] = '0';
                }
                else{
                        s[i] = (char)num;
                }
        }
        return s;
}

CodePudding user response：

This for loop

for(i = 15; i>0; i  ){

is incorrect. Instead of decreasing the variable i it is increased. It seems you mean

for(i = 15; i>=0; i--){

This statement

num = (int)bn1[i]   (int)bn2[i]   co;

should be rewritten like

num = bn1[i] - '0'   bn2[i] - '0'   co;

And this statement

s[i] = (char)num;

should be rewritten like

s[i] = num   '0';

And you are not processing the case when num is equal tp 3 when co is equal to 1 and bn[i] and bn2[i] are both equal to '1'.

Instead of this if statement

co = 0;
if(num == 2){
        co = 1;
        s[i] = '0';
}
else{
        s[i] = (char)num;
}

you could just write

s[i] = num % 2   '0';
cp = num / 2;

CodePudding user response：

@VladFromMoscow has provided a patient and valid answer. But - you could have figured this out on your own, if you were to step through a run of your program, using a debugger.

Here are two Stackoverflow questions about debugging on Linux and on Windows:

• How to debug a C program
• How do you debug a C program on Windows?

If you were to debug the program, stepping through individual commands, you would notice that:

• The loop runs for more than 15 iterations, with j increasing.
• The value of num is rarely between 0 and 3.

and then you could have thought about why that happens, and reached the same conclusion as in Vlad's answer.

Also, and for future reference - most StackOverflow users expect question askers to perform their "due diligence", making reasonable efforts to figure out their problems before asking us for a solution. Now that you know about debuggers - please use one before asking "Why does my program not do what I expected".