form the vowel string ' vstr ' and consonant string ' cstr ' which contains characters in lexicographical order
for ( int i = 0 ; i < SIZE ; i ++ ) { char ch = ( char ) ( i + 97 ) ; for ( int j = 1 ; j <= char_freq [ i ] ; j ++ ) { if ( isVowel ( ch ) ) vstr += ch ; else cstr += ch ; } }