Minor fix to curve_fitting.c

Change-Id: Ib3669a5c4c73178b088dc1e80141f844f807b179

examples/curve_fitting.c

diff --git a/examples/curve_fitting.c b/examples/curve_fitting.c
index 1d1ec9b..3ea2ef1 100644
--- a/examples/curve_fitting.c
+++ b/examples/curve_fitting.c
@@ -155,6 +155,7 @@
 
   double *parameter_pointers[] = { &m, &c };
   int parameter_sizes[] = { 1, 1 };
+  int i;
 
   ceres_problem_t* problem;
 
@@ -164,7 +165,7 @@
   problem = ceres_create_problem();
 
   /* Add all the residuals. */
-  for (int i = 0; i < num_observations; ++i) {
+  for (i = 0; i < num_observations; ++i) {
     ceres_problem_add_residual_block(
         problem,
         exponential_residual,  /* Cost function */