diff --git a/du4/program.c b/du4/program.c
index 0910da6..a20a671 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -48,11 +48,11 @@ int main() {
                 default:
                     if (isdigit(symbol) || symbol == '.'){
                         if (operation == 0)
-                            number1 += symbol;
+                           strcat(number1, symbol+"");
                         else if(!equals)
-                            number2 += symbol;
+                            strcat(number2, symbol+"");
                         else
-                            result += symbol;
+                            strcat(result, symbol+"");
                     }
                     else{
                         printf("CHYBA\n");