CODEWITHSUNDEEP
cprintfscanf
helloman
helloman

Reputation: 23

Why is only the second value entered printed?

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(void)
{
    char wunit[2]; // weight unit
    char hunit[2]; // height unit

    double weight, height;

    printf("Enter the body weight: ");
    scanf("%lf%s", &weight, &wunit); // input weight and unit eg. 150lb

    printf("Enter the height: "); 
    scanf("%lf%s", &height, &hunit); // input height and unit eg. 5.65 ft

    printf("The height unit: %s\n", hunit);
    printf("The weight unit: %s", wunit);

    return 0;
}

This code only prints out the height unit, and not the weight unit. What can I do to fix it?

Upvotes: 1

Views: 125

Answers (4)

pb2q
pb2q

Reputation: 59617

You aren't allowing much space for those two strings: only 2 char for each. Note that C strings also require space for a null-terminating character to mark the end of the string.

With the null-terminating character, your two strings can each only properly hold a single character. When you input e.g. "lb" and "ft", you're using data outside the bounds of your arrays. Change the size of your arrays to (at least) 3, and see if the code prints out both units correctly:

char wunit[3]; // weight unit
char hunit[3]; // height unit

Your code works fine for me with larger arrays.

Upvotes: 2

fbernardo
fbernardo

Reputation: 10104

Because you're trying to but a two character string inside a 2 character array. Strings should always end with '\0', so you should do:

char wunit[3]; // weight unit
char hunit[3]; // height unit

For example, the wunit array would have: ['l', 'b', 0]

Upvotes: 1

asveikau
asveikau

Reputation: 40246

Using %s in scanfis always a bad idea, for the same reason that gets is always a bad idea. You must specify a fixed buffer size; yours, of 2, is absurdly small, but more generally, you cannot control how many characters will be in the input stream, so your program will be susceptible to buffer overflow.

Some ways to fix this:

  • Prefix %s with some length, i.e. "%2s". This will put a maximum length on the amount of characters copied.

  • Use fgets to read the whole line into a string buffer (with some arbitrary maximum), then you have some bounds to the value you wish to read with %s. You can even use sscanf to do it.

  • Use something like readline which will allocate arbitrary amounts of characters to read the line.

Upvotes: 1

JesperE
JesperE

Reputation: 64414

You are missing a \n in the last printf() statement, and since stdout is probably buffered, it is only written to the screen at end-of-line.

Upvotes: 1

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