fgets() / gets() problem while taking input for N strings. Not taking input at initial position

Question

I need to get input for n (user-inputted) strings. For that I start with defining a two-dimensional array char str[ ][ ].
I used for loop getting input from user and have tried gets(), fgets() both. In code example although I used gets().
But it is always taking input for n-1 strings, i.e, 1 less than user want to enter.
Upon further checking I found that program is not taking input for 0th string, i.e., initial string.

My code:

#include <stdio.h>
int main(void){
int i, n;

printf("how many string you want to enter: ");
scanf("%d", &n);

char str[n][60];

printf("start entering strings:\n ");

for(i=0;i<n;i++){     
    gets(str[i]);     //have used here fgets() also
}

puts(str[0]);         //no output for Oth string
return 0;
}

Output:

how many string you want to enter:

User input - 3

how many string you want to enter: 3
start entering strings:

Final Output:

how many string you want to enter: 3
start entering strings:
 abc
bcd

Here program terminates after taking input for only 2 strings and not giving any ouput for puts(str[0]);

Although taking input with scanf() as scanf("%s", str[i]); worked perfectly fine.
I want to know why using gets(), fgets() didn't worked.

To begin with, never ***ever*** use `gets`. It's [a dangerous function](https://stackoverflow.com/questions/1694036/why-is-the-gets-function-so-dangerous-that-it-should-not-be-used) and has therefore even been removed from the C standard. — Some programmer dude, Oct 27 '18 at 10:48
have tried `fgets` also. problem is that it is not taking input for str[0] — Vartika, Oct 27 '18 at 10:59

David Ranieri · Answer 1 · 2018-12-12T20:21:06.183

4

You need to consume the remaining buffer leaved by scanf:

scanf("%d", &n);
char str[n][60];
int c;
while ((c = fgetc(stdin)) != '\n' && c != EOF);
printf("start entering strings:\n ");

You can avoid the ugly flush loop using fgets and strtol instead of scanf:

char buf[32];
int i, n = 0;

printf("how many string you want to enter: ");
if (fgets(buf, sizeof buf, stdin)) {
    n = (int)strtol(buf, NULL, 10);
}

char str[n][60];
printf("start entering strings:\n ");

edited Dec 12 '18 at 20:21

answered Oct 27 '18 at 10:56

David Ranieri

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I didn't understand. – Vartika Oct 27 '18 at 11:08
You have a nice explanation from @Someprogrammerdude in another answer. – David Ranieri Oct 27 '18 at 11:10
2

@asynts, thats why I suggest `fgets` and `strtol`, you can also check if the input is valid using the second parameter, but this is left as an exercise to the OP :) – David Ranieri Oct 27 '18 at 11:36

score 2 · Accepted Answer · answered Oct 27 '18 at 11:04

2

The problem isn't with fgets (or gets for that matter). The problem is your previous call to scanf.

When you end the input of the number with the Enter key, that Enter key will be added to the input buffer as a newline. So after scanf have read the number, the next character left in the input buffer will be that newline. And that's the first character that fgets will read, as an empty line. So it does read all the lines, but the first will be considered empty.

And that's why you don't seem to get any output, because there's no printable characters to print. All you get is an empty line.

answered Oct 27 '18 at 11:04

Some programmer dude

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I think, Biggest problem is- I am using wrong text for learning C. :( – Vartika Oct 27 '18 at 11:13
will community help me in choosing right source? – Vartika Oct 27 '18 at 11:17
2

@Vartika choose the [c] tag and click on "Learn more", there are a lot of tips including resources and books: https://stackoverflow.com/tags/c/info. – David Ranieri Oct 27 '18 at 11:29

fgets() / gets() problem while taking input for N strings. Not taking input at initial position

2 Answers2