Código
void cesar(char* str, int key){ for(; *str; str++) if(*str>='a' && *str<='z') *str = (*str+key-'a')%('z'-'a'+1)+'a'; else if(*str>='A' && *str<='Z'){ *str = (*str+key-'A')%('Z'-'A'+1)+'A'; } } void decryptCesar(char* str, int key){ cesar(str, 'z'-'a'-key+1); }