How to read a numerical value from console window and store it in a character array?

Karthik Agarwal

15y1.8k

Hi,

I need to take some input from console window like 1234 but should be read as decimal value and do whatever you want and store the same in character array. can anyone tell me how can i do this? max width of numerical value is 4 bytes.

Note: I should read from console as decimal value.

12 Replies

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Vulpes15y ago
Accepted answer
The code then would condense down to:

char s[10];
char t[10];

printf("\nInput a string, maximum nine characters : ");
scanf("%9s", s); // ignores any characters after the ninth
printf("\nYou entered %s\n", s);
int i = 0;
char *c = s;
while(*c) t[i++] = *c++;
t[i] = '\0';
printf("\nYou entered %s\n", t);
Sam Hobbs15y ago
It is impossible to "take some input from console window" .... "as decimal value". A console read operation can only read characters, unless your users are willing to do it in a highly inconvenient manner. You must read the numbers as characters and then convert that to a number.

I could explain how to do that but later you say "gets data from application" so I am confused. I suspect that you are not asking for what you actually need. You later say "the application sends me 12345" .... "make the string as 123.45". It is very normal for some computer applications to read floating-point data without a decimal point; the decimal point is at a specified location within the number. So it is entirely possible to read 12345, convert that to a float, then divide that by a specific value. The following are two ways of doing that, but note that they both yield the same result. Floating-point arithmetic is imprecise and therefore division by 100 does not yeild the exact correct answer. I will leave it for you to figure out how to be exact; there is likely a way and I hope you can find it if you need to.
char *s = "12345";
float f = atof(s);
f /= 100;
printf("%f\n", f);

char *s = "12345";
char t[10];
float f, w;
int n = strlen(s);
if (n > 9) {
puts("error");
return;
}
strncpy(t, s, n-2);
t[n-2] = 0;
f = atof(t);
strncpy(t, s+n-2, 2);
t[2] = 0;
w = atof(t);
f += w / 100;
printf("%f\n", f);

As for the later requirements, if you can explain why you must copy a string from one to another, one character at a time, then there is probably a better way to do whatever you need to do. Without a reason not to, the best answer is to use strcpy or strncpy to copy a string. Why can't you do that?
Karthik Agarwal15y ago
actually speaking i don't require
void *vp = (void *)s; this line vp can be directly char pointer. i have restriction only on reading from console window, once it's read it's all your wish. minimize it as such as you can?
Vulpes15y ago
The 's' comes from this line:

char s[10];

I had to create a temporary buffer for vp to point to.

I also created another buffer 't' to copy the chars into to demonstrate the operation was working.

If we were reading the string directly into the first char buffer, then we wouldn't need to copy anything and so wouldn't need the second buffer.
Karthik Agarwal15y ago
where does this "s" come from?
void *vp = (void *)s;

Looks like you just created it to get some address for the other pointer?
Can you tell me a better way, only bcoz of this cause i just can't define one more array or variable?
Vulpes15y ago
I can't see any point in reading the string into a void * as the latter will need to point to a char buffer in any case.

Also, you can't dereference a void *. You have to cast it to a non-generic type such as char * before you can do so.

Anyway, FWIW, here's the code:

char s[10];
char t[10];

printf("\nInput a string, maximum nine characters : ");
void *vp = (void *)s;
scanf("%9s", vp); // ignores any characters after the ninth
printf("\nYou entered %s\n", vp);
char *c = (char *)vp;
int i = 0;
while(*c) t[i++] = *c++;
t[i] = '\0';
printf("\nYou entered %s\n", t);
Karthik Agarwal15y ago
It looks like you mistook what i said, i just wanted to know how to read a string from console window into a void pointer and copy one character after the other into character array. I am asking this check out the possibility of reading it as string as a practice of my own, don't try to compare with the previous discussion which we had.
Vulpes15y ago
In that case you will need to read the console input into the string.

You can do this directly and then convert to a void * if you need that for some other purpose:

char s[7];
printf("\nInput a decimal number, maximum six characters : ");
scanf("%6s", &s); // ignores any characters after the sixth
// validate input
printf("\nYou entered %s", s);
void *vp = (void *)s;

If you entered 123.456, the string would contain 123.45 i.e. a maximum of 6 characters
Karthik Agarwal15y ago
Ok but my problem is that i can't exceed the number of characters represented by the string xxx.xx which must be represented as it is with any decimal which i get from the application. Probably i will rethink on this how it can be done.
And one more thing i wanted is how to read a string from console window into a void pointer and copy character by character into the array? Reply ASAP.

if i enter karthik in console window then i should copy each character one after the other into the character array like 'k' first then 'a' then 'r' then 't' then and so on.
Vulpes15y ago
If the maximum width is 4 bytes and it can contain a decimal point, then you'll need to use the float type which is accurate to 7 or 8 digits.

Is the most important thing here to store the numeric value in the char array exactly as it's entered at the console?

The reason I ask is that you could do it a few lines with this:

char s[10];
float f;
printf("\nInput a decimal number : ";
scanf("%f", &f);
_snprintf(s, 9, "%f", f);
printf("\nYou entered %s", s);

However, the trouble is that, if you enter 123.45, then the final line will print out 123.44999 because it's the internal representation of the float (which isn't usually exact) that gets converted to a string.

To avoid this you could read it as a string and then check that it is in fact a valid float. If that's what you need, then I'll write the code when I have more time.
Karthik Agarwal15y ago
I am working on pure C but in vc++ IDE. In fact mine is a interface file which gets data from application where i will be data like xxx.xx which means that any x can be replaced by any decimal number where as i get the value which needs to be replaced from another application. To answer your question straight yes it can include decimal point. in the above example xxx.xx the application sends me 12345 suppose then i think and make the string as 123.45 and put that in the console window. Hope i answered your question!
Vulpes15y ago
What are you working in : C, unmanaged C++ or C++/CLI?

Also could the number include a decimal point?