minor fixes

main.c

@@ -20,7 +20,7 @@ int main(const int argc, char *argv[]) {
     //manipulate string by cutting of trailing zeros
     char* final_string = manipulate_str(res);
 
-    printf("%s %s %s = %s", argv[1], argv[2], argv[3], final_string);
+    printf("%s %s %s = %s\n", argv[1], argv[2], argv[3], final_string);
     free(final_string);
     return 0;
 }
@@ -67,6 +67,8 @@ double calculate(const CalcStr calc) {
             return calc.first * calc.second;
         case '/':
             return calc.first / calc.second;
+        case '%':
+            return (int)calc.first % (int)calc.second;
         case '^':
             double r = 1;
             for (int i = (int)calc.second; i > 0; i--) {
@@ -81,10 +83,11 @@ double calculate(const CalcStr calc) {
 }
 
 char* manipulate_str(const double input) {
-    const int str_basesize = (int)log10(input) + 16 + 1;
+    const int digit = abs((int)input) == 0 ? 1 : abs((int)input);
+    const int str_basesize = (int)log10(digit) + 16 + 1;
     char *str = malloc(str_basesize * sizeof(char));
     if (str == nullptr) {
-        printf("Failed to allocate the memory");
+        printf("Failed to allocate the memory\n");
         exit(EXIT_FAILURE);
     }
     memset(str, 0, str_basesize);