diff --git a/du4/program.c b/du4/program.c
index e41301f..c2df95b 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -47,12 +47,18 @@ int main() {
                     break;
                 default:
                     if (isdigit(symbol) || symbol == '.'){
-                        if (operation == 0)
-                            strcat(number1, symbol+"");
-                        else if(!equals)
-                            strcat(number2, symbol+"");
-                        else
-                            strcat(result, symbol+"");
+                        if (operation == 0) {
+                            number1[strlen(number1)] = symbol;
+                            number1[strlen(number1)] = '\0';
+                        }
+                        else if(!equals){
+                            number2[strlen(number2)] = symbol;
+                            number2[strlen(number2)] = '\0';
+                        }
+                        else{
+                            result[strlen(result)] = symbol;
+                            result[strlen(result)] = '\0';
+                        }
                     }
                     else{
                         printf("CHYBA\n");