c - Unable to understand scanf() behaviour in the following code -

input -

cometq hvngat 

here's code -

#include <stdio.h> #include <stdlib.h>  #define maxlen 6  main(void) {     char comet[maxlen], group[maxlen];     unsigned long int result[2] = { 1,1 };     short int i, j;      scanf("%s",comet);     scanf("%s",group);     printf("\ncomet's name: %s\ngroup's name: %s",comet,group);     printf("\ncomet's no.: %ld\ngroup's no.: %ld",result[0],result[1]);      = j = 0;     while(comet[i]!='\0' && i<maxlen){         result[0] *= (comet[i] - 'a' + 1);         i++;     }     while(group[j]!='\0' && j<maxlen){         result[1] *= (comet[j] - 'a' + 1);         j++;     }      printf("\ncomet's no.: %ld\ngroup's no.: %ld",result[0],result[1]);     printf("\ncomet's no. mod 47: %ld\ngroup's no. mod 47: %ld",result[0]%47,result[1]%47);      if(result[0]%47 == result[1]%47)         printf("\ngo");     else         printf("\nstay");      exit(0); } 

now, far know, scanf() reads string till whitespace detected. here, output is-

comet's name: cometqhvngat group's name: hvngat comet's no.: 1 group's no.: 1 comet's no.: -534663680 group's no.: 994500 comet's no. mod 47: 43 group's no. mod 47: 27 stay 

but, shouldn't this?

comet = "cometq" & group = "hvngat" 

i don't understand why isn't happening?

in addition, when size of comet 6 bytes, how can store - cometqhvngat?

if want use char array string, need null-terminate it.

in code, array length specified 6, whereas, inputs 6 bytes, leaving no room store terminating null character. that's why, when comet , group passed printf(), they're producing weird output.

a string null-terminated, , based on principle, memory access in case go beyond allocated memory size of comet , group, producing undefined behaviour .

safer alternative:

use fgets() read input, limited size of buffer, rid of last \n character, , you're good-to-go. check man page details.

also, need change format specifier %ld %lu unsigned long int. %ld used signed long int.