Reading multiple user input strings inside a loop

Question

I am currently trying to solve a problem from CodeChef but I am having troubles with using fgets() inside a loop.

The first input (T) is going to be a positive integer containing the number of user inputs.
Then delimited by newline characters, the user is going to input a string below the length of 10 under any circumstances.

So, I've tried this:

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

#define SIZE 10

int main()
{
    int T;
    int diffX, diffY;
    char s[SIZE];

    scanf("%d", &T);

    while (T--){
        fgets(s, SIZE, stdin);
        printf("%s\n", s);
    }
    return 0;
}

However, when I attempted to test the code with the following inputs:

3
Hello
Hi
What

I was only able to input until "Hi" then the program exited successfully (returning 0).

Why is this the case and how can I fix it?

Thank you in advance,
kpark.

scanf doesn't consume the \n from the user entered number. You need to first consume this — simonc
– simonc, Commented Aug 19, 2013 at 20:57
Suggest avoid using both scanf() with fgets(). BTW: Nice tight example of your problem. — chux
– chux, Commented Aug 19, 2013 at 21:00
It takes three strings. The first one consists of just the newline after the 3 (because the scanf() leaves the newline behind). Then you have Hello and Hi as numbers 2 and 3. — Jonathan Leffler
– Jonathan Leffler, Commented Aug 19, 2013 at 21:00

jxh · Accepted Answer · 2013-08-19 20:57:20Z

5

fgets() consumes the newline left behind by the first call to scanf(). So, it is consuming 3 lines, but the first line looks like an empty line to the fgets() loop you have.

You can fix this by using fgets() to get the first line too, and parse the string into a number using sscanf().

fgets(s, SIZE, stdin);
sscanf(s, "%d", &T);
/* ... */

answered Aug 19, 2013 at 20:57

jxh

70.9k8 gold badges116 silver badges204 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

kpark Over a year ago

This has worked well for me and learned a new function. Thank you :)

Jiminion · Accepted Answer · 2013-08-19 20:57:09Z

0

It is counting the read of the T as part of the counting. Add a newline in the scanf.

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

#define SIZE 10



    int main()
    {
        int T;
        int diffX, diffY;
        char s[SIZE];

        scanf("%d\n", &T);

        while (T--){
            fgets(s, SIZE, stdin);
            printf("%s\n", s);
        }
        return 0;
    }

answered Aug 19, 2013 at 20:57

Jiminion

5,1701 gold badge35 silver badges56 bronze badges

4 Comments

Jonathan Leffler Over a year ago

Adding the newline to the scanf() format will work OK here, but would be horrid if the user was typing because the scanf() would not return until some other non-white-space input was entered after the number. Better to use fgets() for all inputs, and sscanf() to process the number.

kpark Over a year ago

This has worked for me and the advice from Jonathan was informative. Thank you!

Jiminion Over a year ago

I agree with Jonathan. Just trying to change the code minimally.

chux Over a year ago

This does not perform consistently is the first time fgets() is called has leading spaces as compare to subsequent calls. If you want to scan in a single '\n, use "%*[\n]". Recall that '\n' in a scanf()` format matches any number of any white space.

dinesh kandpal · Accepted Answer · 2017-03-19 16:02:59Z

Is your Question is about how to read Multiple Strings in C ? Then it can be done by 2 ways :- 1.By declaring two dimensional Array of characters.

//Let say we want 6 strings each of them having max 10 characters.
char set[6][10] ;
for(int i=0;i<6;i++)
scanf("%s",set[i])

2.By declaring one dimensional Array of pointers to character (Notice the naming Conventions), in which each of those pointer pointing to a String.

int main(){

int i,numOfStrings;
char temp[30];

printf("Enter Number of strings in set ");
scanf("%d",&numOfStrings);

//Here We have defined array of pointer that will store each string sepratly.
//Arry of pointer to character.
char *setOfStrings[numOfStrings];

for(i=0;i<numOfStrings;i++)
{
    printf("Enter string ");
    scanf("%s",temp);
    setOfStrings[i]= (char*)malloc(sizeof(temp)); //allocted new memory and gave it to array of pointer
    strcpy(setOfStrings[i],temp);
}

for(i=0;i<numOfStrings;i++)
{
    printf("string = %s \n",setOfStrings[i]);
}
return 0;
}

But that need to understand : In case of array of pointers we may initialize them with String but Can't take as input from Command line like

char *set[2]={"Dinesh","Kandpal"}; //Its valid but you can't do this from command line

for doing so What we do we will create an space dynamically ,store that address in the one of the element in 1-D array of pointers and then whatever value we have scanned copy that content to the another string to the location that we created using malloc

Collectives™ on Stack Overflow

Reading multiple user input strings inside a loop

3 Answers 3

1 Comment

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related