I dont know what is wrong with this program. it's supposed to convert binary to decimal in c

Question

well this program is supposed to convert a binary number to decimal. im new to c and im not very confident in coding C. tried and coded this program but doesnt run properly. and I have no idea what part is wrong here. need some help to complete this program. thanks

binaryToDecimal(char str[]) {
    for(int i = strlen(str)-i; i>=0; i--) {
        if(str[i] == 48 || str[i] == 49) {
            int tmp = pow(2, counter);
            int sum= str[i]*tmp;
            counter++;
            answer += sum;
        } else if(str[i]>49 || str[i]<48) {
            printf("error");
        }
    }
    printf("%d", &answer);
}

this may be of help: http://stackoverflow.com/questions/9852917/convert-binary-to-hex-to-decimal — jev, Oct 05 '13 at 00:25
Please explain *doesn't run properly*. What input do you give it? What output do you expect? What output did you actually get? — abelenky, Oct 05 '13 at 00:26
"doesn't run properly" is not a problem description that is useful. What exactly does "doesn't run properly" mean? In what way is it not proper? If you want us to help you, you need to be *specific about the problem you're having*. After all, you know what it is, or you wouldn't be posting here for help. Why not explain it to us so we know too? — Ken White, Oct 05 '13 at 00:30

score 2 · Answer 1 · answered Oct 05 '13 at 00:27

2

This phrase doesn't make sense:

int i = strlen(str)-i;

i hasn't been initialized yet, but you're using it in the expression!

I believe you meant:

int i = strlen(str)-1;   // ONE ... not I

answered Oct 05 '13 at 00:27

abelenky

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`answer` is too not initialized. – haccks Oct 05 '13 at 00:29

score 2 · Answer 2 · answered Oct 05 '13 at 00:31

2

str[i] is a character, either '1' or '0' which as you have it is equal to 48 and 49 as integers. So you want to convert them to 1 and 0 them do the multiplication.

sum = (str[i] - 48) * tmp;

answered Oct 05 '13 at 00:31

Musa

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score 0 · Answer 3 · answered Oct 05 '13 at 00:57

Assuming all variables have been initialised to sensible values and str holds the input. The following code should work, although it is not particularly efficient. You can use '0' and '1' instead of more obscure 48 and 49.

for (i = strlen(str)-1, j = 0; i >= 0; --i, ++j) { 

   if (str[i] != '0' && str[i] != '1') {
       printf("ERROR: unxepected input\n");
       exit(EXIT_FAILURE);
   }

   if (str[i] == '1')
       sum += pow(2, j);
}

when printing the result provide the value and not it's address, e.g.

printf("%d\n", sum);  // (!) not &sum

I dont know what is wrong with this program. it's supposed to convert binary to decimal in c

3 Answers3