Declare the iterator variable outside the loop in curve_fitting.c

Change-Id: I4ce703c8d6a6deb3aebaccd3cd5d916c7aa4f92e

examples/curve_fitting.c

diff --git a/examples/curve_fitting.c b/examples/curve_fitting.c
index 47b551e..a2fb5b9 100644
--- a/examples/curve_fitting.c
+++ b/examples/curve_fitting.c
@@ -155,7 +155,8 @@
   int parameter_sizes[] = { 1, 1 };
 
   ceres_problem_t* problem = ceres_create_problem();
-  for (int i = 0; i < num_observations; ++i) {
+  int i;
+  for (i = 0; i < num_observations; ++i) {
     ceres_problem_add_residual_block(
         problem,
         exponential_residual,  /* Cost function */