完成并修改正确必做题

exp1/badcount.c

@@ -0,0 +1,59 @@
+#include <pthread.h>
+#include <time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+void *increase(void *vargp);
+void *decrease(void *vargp);
+int cnt = 0;
+
+
+int main(int argc, char **argv)
+{
+    unsigned int niters;
+    pthread_t t1,t2;
+    
+    if (argc != 2)
+    {
+        printf("Usage: %s <niters>\n", argv[0]);
+        exit(2);
+    }
+    niters = atoll(argv[1]);
+    
+    pthread_create(&t1,NULL,increase,(void *)niters);
+    pthread_create(&t2,NULL,decrease,(void *)niters);
+    pthread_join(t1,NULL);
+    pthread_join(t2,NULL);
+    
+    if (cnt != 0)
+    {
+        printf("Error! cnt=%d\n", cnt);
+    }
+    else
+    {
+        printf("Correct! cnt=%d\n", cnt);
+    }
+    exit(0);
+}
+
+void *increase(void *vargp)
+{
+    unsigned i ,niters = (unsigned int)vargp;
+    for ( i = 0; i < niters; i++)
+    {
+        cnt++;
+    }
+    return NULL;
+}
+
+void *decrease(void *vargp)
+{
+    unsigned i, niters = (unsigned int)vargp;
+    for ( i = 0; i < niters; i++)
+    {
+        cnt--;
+    }
+    return NULL;
+}