#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#define NUMQUEST 20
#define NUMLIMIT 11

int main(void) {
 char ops[] = {'+', '-', '*'};
 int correct = 0;
 struct timeval start, end;
 gettimeofday(&start, NULL);
 srandom((unsigned) start.tv_sec);
 for (int i=0; i<NUMQUEST; i++) {
  int a = random() % NUMLIMIT, b = random() % NUMLIMIT, c;
  char op = ops[random() % 3];
  if (op == '-' && a-b < 0) {int x = a; a = b; b = x; }
  printf("%2d %c %2d = ", a, op, b);
  _Bool truth;
  if (scanf("%d", &c) != 1) truth = 0;
  else switch (op) {
   case '+': truth = (c == a+b); break;
   case '-': truth = (c == a-b); break;
   case '*': truth = (c == a*b); break;
  }
  if (truth) {correct++; printf("   CORRECT!\n"); }
  else {printf("   WRONG!\n"); }
 }
 gettimeofday(&end, NULL);
 double timeSpent = end.tv_sec - start.tv_sec + (end.tv_usec - start.tv_usec) / 1000000.0;
 printf("You got %d out of %d problems correct in %.6f seconds.\n", correct, NUMQUEST, timeSpent);
 return 0;
}