diff --git a/5-10 b/5-10
index d3f5c5526d4ab6cf9d239b2aa48d64619dd2684b..440de58a990625e4380c3c18e956a26bb54e12b0 100644
--- a/5-10
+++ b/5-10
@@ -3,35 +3,35 @@
 
 int main()
 {
-    int sc=0;
-	scanf("%d",&sc);
-	int t=sc/10;
-	switch(t)
-	{
-		case 10:case 9:
-	    printf("Letter grade: A");
-		break;
-		
-		case 8:
-		printf("Letter grade: B");
-		break;
-		
-		case 7:
-		printf("Letter grade: C");
-		break;
-		
-		case 6:
-		printf("Letter grade: D");
-		break;
-		
-		case 0 ... 5:
-		printf("Letter grade: F");
-		break;
-		
-		default:
-		printf("Error, grade must be between 0 and 100.");
-		break;
-			
-	 } 
+    int sc = 0;
+    scanf("%d", &sc);
+    if (sc > 100 || sc < 0) {
+        printf("Error, grade must be between 0 and 100.");
+        return 0;
+    }
+    int t = sc / 10;
+    switch (t) {
+    case 10:
+    case 9:
+        printf("Letter grade: A");
+        break;
+
+    case 8:
+        printf("Letter grade: B");
+        break;
+
+    case 7:
+        printf("Letter grade: C");
+        break;
+
+    case 6:
+        printf("Letter grade: D");
+        break;
+
+    case 0 ... 5:
+        printf("Letter grade: F");
+        break;
+
+    }
     return 0;
 }
\ No newline at end of file