Getting multiple strings as inputs

Now before getting to the specified problem lets see what the actual problem is:

• Problem with scanf()

  The problem with scanf() is that it is really bad at managing overflows. And in case of chars or char sequences the newline character is read on the press of enter key in the subsequent scanning. There are numerous instances on SO that concern this problem. scanf() leaves the new line char in buffer? and Problems with scanf

• Problem with gets()

  The biggest drawback is that here you need to know the size of input before-hand. If you know your input extremely well, you may use it (Still I won't recommend). Why is the gets function so dangerous that it should not be used?

• Problem with fgets()

  There are two really common problems with fgets()

  The syntax of fgets() is:

        char *fgets(char *restrict s, int n, FILE *restrict stream);`
  

  and generally used like

        fgets(char_array,100,stdin)
  

  1. First problem arises when the input is bigger than the integer n provided in the fgets() second parameter. When the input in the buffer is bigger than n it will strip off 1st n chars and allocate it the char pointer which might be a char array. But what about remaining chars? They still are there in the input buffer and will be allocated to next fgets(). Messing things up.

  2. Second problem is that every time a new line feed is allocated to the end of char sequence when the input is smaller than the int n-1.

But if we think for a while the problems with fgets() can be tackled with a simple trick.

• Just check for the last character in the char sequence which has been recently allocated. If it is new line, replace it by NULL. Else we know that the input was more than that int provided inside fgets(). So all we have to do is eat up the remaining chars in the input buffer.

Here is an example:

   char str1[5];
   char str2[5];
   fgets(str1,5,stdin);

   if(strlen(str1)>0){//to avoid Undefined Behavior in case of null byte input

       if(str1[strlen(str1)-1]=='\n'){

           str1[strlen(str1)-1]='\0';
       }
       else{

           while((getchar())!='\n');//eating the remaing chars in the buffer
       } 
   }

   fgets(str2,5,stdin);


   if(strlen(str2)>0){

      if(str2[strlen(str2)-1]=='\n'){

         str2[strlen(str2)-1]='\0';

      }
      else{

         while((getchar())!='\n');
      }

   }
   printf("\n1.%s\n2.%s",str1,str2);

You could even convert strings you got using fgets to float and integers using things like strol or sscanf, but beware they may not show independent behavior.

Now coming back to the solution to your problem:

#include <stdio.h>
#include <string.h>

int main(){
    char s1[100],s2[100],s3[100];
    char ch[2];//make ch atleast 2 char wide

    fgets(s1,100,stdin);
     if(strlen(s1)>0){

          if(s1[strlen(s1)-1]=='\n'){

             s1[strlen(s1)-1]='\0';

          }
          else{

             while((getchar())!='\n');
          }

    }

   fgets(s2,100,stdin);
     if(strlen(s2)>0){

          if(s2[strlen(s2)-1]=='\n'){

             s2[strlen(s2)-1]='\0';

          }
          else{

             while((getchar())!='\n');
          }

    }

   fgets(s3,100,stdin);
     if(strlen(s3)>0){

          if(s3[strlen(s3)-1]=='\n'){

             s3[strlen(s3)-1]='\0';

          }
          else{

             while((getchar())!='\n');
          }

    }    

    fgets(ch,2,stdin);
      if(strlen(ch)>0){

          if(ch[strlen(ch)-1]=='\n'){

              ch[strlen(ch)-1]='\0';

          }
          else{

              while((getchar())!='\n');
          }

     }

    if(isalpha(ch[0]) && (s1[0]==ch[0] || s2[0]==ch[0] || s3[0]==ch[0]))
        printf("yes");
    else
        printf("no");

        return 0;
}