Update expr.c

Filling the stack should start from element with index 0.

Author: JebediahS

chapter_5/exercise_5_10/expr.c

@@ -95,7 +95,7 @@ int main(int argc, char *argv[]) {
 
 float pop(void) {
     if (stack_pointer > 0) {
-        return stack[stack_pointer--];
+        return stack[--stack_pointer];
     }
 
     printf("Error: the stack is empty.\n");
@@ -104,7 +104,7 @@ float pop(void) {
 
 void push(float element) {
     if (stack_pointer < STACK_SIZE) {
-        stack[++stack_pointer] = element;
+        stack[stack_pointer++] = element;
     } else {
         printf("Error: the stack is full.\n");
     }