c - printing common characters in three strings -

q) write c program takes input 3 strings, each of maximum 30 characters, , prints common characters present in 3 strings. each string can have different number of characters.

the code have written is:

#include<stdio.h>  int main() {     int c1=0 , c2=0, c3=0 ,i,x;       int count1[26]={0} , count2[26]={0} , count3[26]={0};       char st1[30],st2[30],st3[30];       printf("enter string1: ");       gets(st1);       printf("\n enter string2: ");       gets(st2);       printf("\n enter string3: ");     gets(st3);       while(st1[c1]!='\0')       {         count1[st1[c1]-'a']++;           c1++;     }       while(st2[c2]!='\0')         {         count2[st2[c2]-'a']++;            c2++;     }      while(st3[c3]!='\0')     {         count3[st3[c3]-'a']++;         c3++;     }      for(i=0;i<26;i++)     {         if(count1[i]!=0 && count2[i]!=0 && count3[i]!=0)         {             if (count1[i]<count2[i] && count1[i]<count3[i])             {                 for(x=0;x<count1;x++)                 {                     printf("\n %c ",x+'a');                 }             }             else if(count2[i]< count1[i] && count2[i]< count3[i])             {                 for(x=0;x<count2;x++)                 {                     printf("%c",x+'a');                 }             }             else             {                 for(x=0;x<count3;x++)                 {                     printf("%c",x+'a');                 }             }         }     } } 

but when run code in codeblocks,continuous randomcharacters occuring continous beep beep sound till shut down system. can me this?

there various errors in code.

• when print common characters, loop is:

  for (x = 0; x < count1; x++) ... 

  but count1 address of array, huge number. loop runs longer expect; accesses memory locations beyond count[25] contain random data (at least none algorithm can make sense of) , prints it. (the beep sound comes printing character ascii code 7, alert or bell code '\a'. if on ms-dos, you'd see happy black , white faces too.)

  the correct loop runs number of letters stored in count1 letter i.

  for (x = 0; x < count1[i]; x++) ... 

• when count letters, increase

  count1[st1[c1] - 'a']++; 

  this evoke dreaded undefined behaviour when st1[c1] - 'a' not in range 0 25. can happen, e.g. if string "new york". either need check character lies in correct range or need extend solution full range of characters. (note assignment talks characters, not letters.)

• when print common characters, don't print them correctly:

  printf("%c", x + 'a'); 

  here, x running 0 number of occurrences of letter i. if common characters thee o's, print "abc". should print i + 'a'. (this logic error, not can crash program.)