Code giving runtime error in codeforce prob 474 A - c

Question

I am a beginner in codeforces. I am stuck in problem 474 A where I am getting runtime error. But I can't any fault in it. I use C. Here is my code:
#include<stdio.h>
int main()
{
int a, i, j, b, arr[102];
char ch, str2[101], c;
char str1[30] = "qwertyuiopasdfghjkl;zxcvbnm,./";
for (i = 0; i<30; i++)
arr[(str1[i])] = i;
scanf("%c%s", &ch, str2);
if (ch == 'R')
{
for (i = 0; str2[i]; i++)
{
printf("%c", str1[(arr[str2[i]] - 1)]);
}
printf("\n");
}
else {
for (i = 0; str2[i]; i++)
{
printf("%c", str1[(arr[str2[i]] + 1)]);
}
printf("\n");
}
return 0;
}
Can you find what is wrong in it?

Answer 1

Please try this, if I understood the problem correctly this works.
// MOLE is typing to the right or to the left of 3 rows of keys
// qwertyuiop
// asdfghjkl;
// zxcvbnm,./
// encoded as: !qwertyuiop!asdfghjkl;!zxcvbnm,./!
// where '!' detects input errors
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main( void )
{
int i;
char ch;
char str2[101];
char kstr1[50];
char *poschar; // pointer to char
int int_poschar = 0;
int translated_position = 0;
int right = 0;
int left = 0;
strcpy( kstr1, "!qwertyuiop!asdfghjkl;!zxcvbnm,./!" );
printf( "\n Please enter R or L and press enter\n" );
scanf( " %c ", &ch );
ch = toupper( ch );
if ( ch == 'R' || ch == 'L' ) ; // good input say nothing
else
{
printf( "\nPlease try again with L or R ( or l or r ) " );
exit( 0 );
}
printf( "\n Please enter a word and press enter\n" );
scanf( " %100s", str2 );
strcpy( str2, strlwr( str2 ) );
if ( ch == 'R' )
{
printf( "\nRIGHT translate:\n%s\n", str2 );
right = 1;
}
else if ( ch == 'L' )
{
printf( "\nLEFT translate:\n%s\n", str2 );
left = 1;
}
getchar( );
for ( i = 0; str2[i]; i++ )
{
poschar = strchr( kstr1, str2[i] );
if ( poschar != NULL )
{
int_poschar = poschar - kstr1; // find prev pos in array
if ( right )
translated_position = int_poschar - 1;
else if ( left )
translated_position = int_poschar + 1;
else
{
printf( "\n you've got a bug !" );
exit( 0 );
}
if ( kstr1[translated_position] == '!' )
{
if ( right )
printf( "\n not possible, MOLE wrote 1 key to the right" );
else
printf( "\n not possible, MOLE wrote 1 key to the left" );
getchar( );
exit( 0 );
}
printf( "%c", kstr1[int_poschar - 1] );
} // endif ( poschar != NULL )
}
exit( 0 );
}