$ ./t_scan_float                                                               
[0] 1e1 10.000000
fail: scan_float: [1] 1.000000 != 0.100000
$ gdb t_scan_float
(gdb) r
Starting program: ./t_scan_float 
[0] 1e1 10.000000
fail: scan_float: [1] 1.000000 != 0.100000

Program exited with code 01.
(gdb) b scan_float
Breakpoint 1 at 0x80486c6: file scan_float.c, line 15.
(gdb) r
Starting program: ./t_scan_float 

Breakpoint 1, scan_float (str=0x8048940 "1e1", f=0xbfbfeaa0) at scan_float.c:15
15        ptr = str;
(gdb) c
Continuing.
[0] 1e1 10.000000

Breakpoint 1, scan_float (str=0x8048944 "1e-1", f=0xbfbfeaa0)
    at scan_float.c:15
15        ptr = str;
(gdb) q
The program is running.  Exit anyway? (y or n) y