CODEWITHSUNDEEP
carrays
fbid
fbid

Reputation: 1570

Reading a char array from stdin

I'm trying to read a constant length string as an array of c for 8 times. Each time i override the content of the previously read array.

The code seems to be working at the first loop cycle, but then as you can see below, I get some weird output. What am I missing?

CODE:

#include <stdio.h>

#define MAX_READ_CYCLES 8
#define MAX_STRING_LENGTH 4

int main(){

  int i, cycles;
  char a[MAX_STRING_LENGTH+1];


  /***************************************************
   * BEGIN Read logic
   ***************************************************/

  for(cycles=0; cycles < MAX_READ_CYCLES; cycles++){

    i=0;

    printf("\nEnter a string: ");

    while(i < MAX_STRING_LENGTH){
      a[i] = getc(stdin);
      i++;
    }

    a[i] = '\0'; //string end character

    fflush(stdin); //cleaning the buffer

    printf("String you entered: %s\n", a);

  }

  /***************************************************
   * END
   ***************************************************/


   return 0;
}

OUTPUT:

Enter a string: cccc
String you entered: cccc

Enter a string: cccc
String you entered: 
ccc

Enter a string: String you entered: 

Enter a string:

Upvotes: 0

Views: 5618

Answers (3)

tdao
tdao

Reputation: 17668

Consider a few issues:

a[i] = getc(stdin); would take the previous Enter as an input, and so you'd loose one character.

You can try scanf( " %c", &a[i] ); instead, which would eliminate the buffered Enter character, and also the need for fflush() function.

In your case, it might not be necessary, but usually I'd reset the character array before each read iteration using memset:

memset( a, 0, sizeof( a ) ); // this requires <string.h>

Enter a string: cccc
String you entered: cccc

Enter a string: cccc
String you entered: 
ccc    # one `c` is missing because the input buffer looks like this `<Enter>cccc`, in which `<Enter>` is left over from previous input.

Enter a string: 

String you entered: c # display `c` because input buffer contains `c<Enter><Enter><Enter>`, in which `c<Enter>` is left over from previous input.

Upvotes: 1

M.M
M.M

Reputation: 141586

fflush(stdin); causes undefined behaviour. Replace that line with:

int ch;
while ( (ch = getchar()) != '\n' && ch != EOF ) {}

Your code has another logical issue. It always reads 4 characters , even if the person presses Enter first. So if someone types hi and presses Enter then it keeps waiting until the next Enter press.

You may want to modify the while loop to also break if the key '\n' was just entered. In this scenario you would NOT go on to clean the input as described above.

Upvotes: 3

Dylan Kirkby
Dylan Kirkby

Reputation: 1427

Your code segment reads in exactly four characters including newlines. Use the scanf() library function to input string characters into a

#include <stdio.h>

#define MAX_READ_CYCLES 8
#define MAX_STRING_LENGTH 4

int main(){

  int i, cycles;
  char a[MAX_STRING_LENGTH+1];


  /***************************************************
   * BEGIN Read logic
   ***************************************************/

  for(cycles=0; cycles < MAX_READ_CYCLES; cycles++){

    i=0;

    printf("\nEnter a string: ");

    scanf("%s", a);

    fflush(stdin); //cleaning the buffer

    printf("String you entered: %s\n", a);

  }

  /***************************************************
   * END
   ***************************************************/


   return 0;
}

Upvotes: 0

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