How to use a step rather than keep referring to a watchpoint in GDB

I've used the following steps to keep track of variables in GDB and it works great for me:

 1. set some breakpoints
 2. run
 3. watch a variable
 4. continue

      

        
        
        
      

    

However, in this gdb youtube tutorial (starting at 12:10), the author uses this step instead of continuing to invoke watchpoint messages, a position I was unable to reproduce.

The example code was copied from the tutorial:

int main(int argc, char *argv[])
{
  int sum, i;
  char string[120];

  sum=0;
  strcpy(string, "Hello!");

  for(i=0;i<10;i++) {
    sum+=i;
    sum=square(sum, i);
  }
  printf("sum=%d\n", sum);
  return 0;
}

int square(int big, int temp)
{
  int i;
  i=big;
  if(big>10) i=i%10;
  return(i*temp);
}

      

        
        
        
      

    

Here are the steps I tried to call watchpoint "step" but failed (That is, even if I set the watchpoint but the message "Old value =" and "New value =" was not shown):

 1. start
 2. step to main
 3. watch i
 4. step several times but none of watchpoint message was shown

      

        
        
        
      

    

What do I need to do to get it to work with a "step"? Thank.

Here is my working environment:

gdb version: 7.11.1
OS: Ubuntu 16.04 on VMware player 12 in Win10

Edited:
1. This is the code I used "continue" and worked fine with.

syuan@ubuntu:~/Downloads$ gdb test

(gdb) b main
Breakpoint 1 at 0x4005ae: file test.c, line 8.

(gdb) run
Starting program: /home/syuan/Downloads/test 

Breakpoint 1, main (argc=1, argv=0x7fffffffde48) at test.c:8
8   {
(gdb) watch i
Hardware watchpoint 2: i
(gdb) c
Continuing.

Hardware watchpoint 2: i

Old value = 0
New value = 1
0x0000000000400615 in main (argc=1, argv=0x7fffffffde48) at test.c:15
15    for(i=0;i<10;i++) {
(gdb) c
Continuing.

Hardware watchpoint 2: i

Old value = 1
New value = 2
0x0000000000400615 in main (argc=1, argv=0x7fffffffde48) at test.c:15
15    for(i=0;i<10;i++) {
(gdb) c
Continuing.

Hardware watchpoint 2: i

Old value = 2
New value = 3
0x0000000000400615 in main (argc=1, argv=0x7fffffffde48) at test.c:15

      

        
        
        
      

    

2. This is the code that I used "step" or "next" but had no success.

syuan@ubuntu:~/Downloads$ gdb test

(gdb) b main
Breakpoint 1 at 0x4005ae: file test.c, line 8.
(gdb) start
Temporary breakpoint 2 at 0x4005ae: file test.c, line 8.
Starting program: /home/syuan/Downloads/test 

Breakpoint 1, main (argc=1, argv=0x7fffffffde48) at test.c:8
8   {
(gdb) step
12    sum=0;
(gdb) watch i
Hardware watchpoint 3: i
(gdb) step
13    strcpy(string, "Hello!");
(gdb) step
15    for(i=0;i<10;i++) {
(gdb) step
16      sum+=i;
(gdb) step
17      sum=square(sum, i);
(gdb) step
square (big=0, temp=0) at test.c:26
26    i=big;
(gdb) step
27    if(big>10) i=i%10;
(gdb) step
28    return(i*temp);
(gdb) step
29  }
(gdb) step
main (argc=1, argv=0x7fffffffde48) at test.c:15
15    for(i=0;i<10;i++) {
(gdb) step
16      sum+=i;
(gdb) step
17      sum=square(sum, i);
(gdb) step
square (big=1, temp=1) at test.c:26
26    i=big;
(gdb) step
27    if(big>10) i=i%10;
(gdb) step
28    return(i*temp);
(gdb) step
29  }
(gdb) step
main (argc=1, argv=0x7fffffffde48) at test.c:15
15    for(i=0;i<10;i++) {
(gdb) step
16      sum+=i;
(gdb) step
17      sum=square(sum, i);
(gdb) step
square (big=3, temp=2) at test.c:26
26    i=big;
(gdb) step
27    if(big>10) i=i%10;
(gdb) step
28    return(i*temp);
(gdb) step
29  }
(gdb) step
main (argc=1, argv=0x7fffffffde48) at test.c:15
15    for(i=0;i<10;i++) {
(gdb) next
16      sum+=i;
(gdb) next
17      sum=square(sum, i);
(gdb) next
15    for(i=0;i<10;i++) {
(gdb) next
16      sum+=i;
(gdb) next
17      sum=square(sum, i);
(gdb) next
15    for(i=0;i<10;i++) {
(gdb) next
16      sum+=i;
(gdb) info watchpoint
Num     Type           Disp Enb Address            What
3       hw watchpoint  keep y                      i

      

        
        
        
      

    

Edited again

I tested it on an online gdb tool with gdb 7.7.1, a Linux server with gdb 7.11.1, and a Linux PC as the HOST OS. They all work, leading to speculation that this might be a problem for the VM, but this requires additional verification.