C Program Time Conversion
I came upon this Time Conversion Program in HackerRank, I was surprised the way how the program is compiled in HackerRank (or could be my misunderstanding of C).
#include <stdio.h>
int main() {
int hh, mm, ss;
char tt[2];
scanf("%d:%d:%d%s", &hh, &mm, &ss, tt);
printf("%dn", hh);
if(strcmp(tt, "PM") == 0 && hh != 12) hh += 12;
if(strcmp(tt, "AM") == 0 && hh == 12) hh = 0;
printf("%02d:%02d:%02d", hh, mm, ss);
return 0;
}
The above program, when I ran in my computer, using MinGW 32-bit GCC Compiler, I was getting the value of hh as zero.
Fine, I thought could be compiler issue and ran the code in IDEONE, same results.
But when I ran this same code with HackerRank, all testcases were passed, I have no idea, how this is working here?
I am confused at this stage, am I doing this right?
c time
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
add a comment |
I came upon this Time Conversion Program in HackerRank, I was surprised the way how the program is compiled in HackerRank (or could be my misunderstanding of C).
#include <stdio.h>
int main() {
int hh, mm, ss;
char tt[2];
scanf("%d:%d:%d%s", &hh, &mm, &ss, tt);
printf("%dn", hh);
if(strcmp(tt, "PM") == 0 && hh != 12) hh += 12;
if(strcmp(tt, "AM") == 0 && hh == 12) hh = 0;
printf("%02d:%02d:%02d", hh, mm, ss);
return 0;
}
The above program, when I ran in my computer, using MinGW 32-bit GCC Compiler, I was getting the value of hh as zero.
Fine, I thought could be compiler issue and ran the code in IDEONE, same results.
But when I ran this same code with HackerRank, all testcases were passed, I have no idea, how this is working here?
I am confused at this stage, am I doing this right?
c time
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
3
You are 1-char short onchar tt[2];You forgot about the nul-terminating character. You need at minimumchar tt[3] = "";to holdAMorPM(the initialization is just good practice)
– David C. Rankin
Apr 12 '16 at 10:32
@DavidC.Rankin, how does variable hh return zero, just because of char pointer is having a shorter storage space? and how does it run on hackerrank?
– cs1193
Apr 12 '16 at 10:35
3
It runs poorly. You invoke undefined behavior.
– Lundin
Apr 12 '16 at 10:41
2
@cs1193 It depends on the layout of variables on the stack. Ifttis right beforehh, the final nul character will overwrite the first byte ofhh, setting it to zero on a little endian architecture.
– nwellnhof
Apr 12 '16 at 11:01
add a comment |
I came upon this Time Conversion Program in HackerRank, I was surprised the way how the program is compiled in HackerRank (or could be my misunderstanding of C).
#include <stdio.h>
int main() {
int hh, mm, ss;
char tt[2];
scanf("%d:%d:%d%s", &hh, &mm, &ss, tt);
printf("%dn", hh);
if(strcmp(tt, "PM") == 0 && hh != 12) hh += 12;
if(strcmp(tt, "AM") == 0 && hh == 12) hh = 0;
printf("%02d:%02d:%02d", hh, mm, ss);
return 0;
}
The above program, when I ran in my computer, using MinGW 32-bit GCC Compiler, I was getting the value of hh as zero.
Fine, I thought could be compiler issue and ran the code in IDEONE, same results.
But when I ran this same code with HackerRank, all testcases were passed, I have no idea, how this is working here?
I am confused at this stage, am I doing this right?
c time
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
I came upon this Time Conversion Program in HackerRank, I was surprised the way how the program is compiled in HackerRank (or could be my misunderstanding of C).
#include <stdio.h>
int main() {
int hh, mm, ss;
char tt[2];
scanf("%d:%d:%d%s", &hh, &mm, &ss, tt);
printf("%dn", hh);
if(strcmp(tt, "PM") == 0 && hh != 12) hh += 12;
if(strcmp(tt, "AM") == 0 && hh == 12) hh = 0;
printf("%02d:%02d:%02d", hh, mm, ss);
return 0;
}
The above program, when I ran in my computer, using MinGW 32-bit GCC Compiler, I was getting the value of hh as zero.
Fine, I thought could be compiler issue and ran the code in IDEONE, same results.
But when I ran this same code with HackerRank, all testcases were passed, I have no idea, how this is working here?
I am confused at this stage, am I doing this right?
c time
c time
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
edited Aug 11 '17 at 20:14
Martijn Pieters♦
724k14325452348
724k14325452348
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
asked Apr 12 '16 at 10:27
cs1193cs1193
84611222
84611222
3
You are 1-char short onchar tt[2];You forgot about the nul-terminating character. You need at minimumchar tt[3] = "";to holdAMorPM(the initialization is just good practice)
– David C. Rankin
Apr 12 '16 at 10:32
@DavidC.Rankin, how does variable hh return zero, just because of char pointer is having a shorter storage space? and how does it run on hackerrank?
– cs1193
Apr 12 '16 at 10:35
3
It runs poorly. You invoke undefined behavior.
– Lundin
Apr 12 '16 at 10:41
2
@cs1193 It depends on the layout of variables on the stack. Ifttis right beforehh, the final nul character will overwrite the first byte ofhh, setting it to zero on a little endian architecture.
– nwellnhof
Apr 12 '16 at 11:01
add a comment |
3
You are 1-char short onchar tt[2];You forgot about the nul-terminating character. You need at minimumchar tt[3] = "";to holdAMorPM(the initialization is just good practice)
– David C. Rankin
Apr 12 '16 at 10:32
@DavidC.Rankin, how does variable hh return zero, just because of char pointer is having a shorter storage space? and how does it run on hackerrank?
– cs1193
Apr 12 '16 at 10:35
3
It runs poorly. You invoke undefined behavior.
– Lundin
Apr 12 '16 at 10:41
2
@cs1193 It depends on the layout of variables on the stack. Ifttis right beforehh, the final nul character will overwrite the first byte ofhh, setting it to zero on a little endian architecture.
– nwellnhof
Apr 12 '16 at 11:01
3
3
You are 1-char short on
char tt[2]; You forgot about the nul-terminating character. You need at minimum char tt[3] = ""; to hold AM or PM (the initialization is just good practice)– David C. Rankin
Apr 12 '16 at 10:32
You are 1-char short on
char tt[2]; You forgot about the nul-terminating character. You need at minimum char tt[3] = ""; to hold AM or PM (the initialization is just good practice)– David C. Rankin
Apr 12 '16 at 10:32
@DavidC.Rankin, how does variable hh return zero, just because of char pointer is having a shorter storage space? and how does it run on hackerrank?
– cs1193
Apr 12 '16 at 10:35
@DavidC.Rankin, how does variable hh return zero, just because of char pointer is having a shorter storage space? and how does it run on hackerrank?
– cs1193
Apr 12 '16 at 10:35
3
3
It runs poorly. You invoke undefined behavior.
– Lundin
Apr 12 '16 at 10:41
It runs poorly. You invoke undefined behavior.
– Lundin
Apr 12 '16 at 10:41
2
2
@cs1193 It depends on the layout of variables on the stack. If
tt is right before hh, the final nul character will overwrite the first byte of hh, setting it to zero on a little endian architecture.– nwellnhof
Apr 12 '16 at 11:01
@cs1193 It depends on the layout of variables on the stack. If
tt is right before hh, the final nul character will overwrite the first byte of hh, setting it to zero on a little endian architecture.– nwellnhof
Apr 12 '16 at 11:01
add a comment |
1 Answer
1
active
oldest
votes
With the changes made to allow space in tt to accommodate the nul-terminating character, the code functions well in making conversions to military time. By initializing tt to zero all elements during declaration/definition, you have insure tt will be nul-terminated when AM or PM are added. e.g.
#include <stdio.h>
#include <string.h>
int main (void) {
int hh, mm, ss;
char tt[3] = "";
printf (" enter time in HH:MM:SS AM/PM: ");
if (scanf ("%d:%d:%d %[^n]%*c", &hh, &mm, &ss, tt) != 4) {
fprintf (stderr, "error: invalid read of time.n");
}
hh = (strcmp (tt, "PM") == 0 && hh != 12) ? hh + 12 : hh;
if (strcmp (tt, "AM") == 0 && hh == 12) hh = 0;
printf (" %02d:%02d:%02dnn", hh, mm, ss);
return 0;
}
Example Use/Output
$ ./bin/tmread
enter time in HH:MM:SS AM/PM: 11:59:04 PM
23:59:04
Look it over and let me know if you have any questions.
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
Agreed, it can always be replaced with"%[^n]%*c"which is probably the better solution. It was originally left as%ssince we were dealing withAM,PMin a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...
– David C. Rankin
Apr 14 '16 at 16:11
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
With the changes made to allow space in tt to accommodate the nul-terminating character, the code functions well in making conversions to military time. By initializing tt to zero all elements during declaration/definition, you have insure tt will be nul-terminated when AM or PM are added. e.g.
#include <stdio.h>
#include <string.h>
int main (void) {
int hh, mm, ss;
char tt[3] = "";
printf (" enter time in HH:MM:SS AM/PM: ");
if (scanf ("%d:%d:%d %[^n]%*c", &hh, &mm, &ss, tt) != 4) {
fprintf (stderr, "error: invalid read of time.n");
}
hh = (strcmp (tt, "PM") == 0 && hh != 12) ? hh + 12 : hh;
if (strcmp (tt, "AM") == 0 && hh == 12) hh = 0;
printf (" %02d:%02d:%02dnn", hh, mm, ss);
return 0;
}
Example Use/Output
$ ./bin/tmread
enter time in HH:MM:SS AM/PM: 11:59:04 PM
23:59:04
Look it over and let me know if you have any questions.
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
Agreed, it can always be replaced with"%[^n]%*c"which is probably the better solution. It was originally left as%ssince we were dealing withAM,PMin a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...
– David C. Rankin
Apr 14 '16 at 16:11
add a comment |
With the changes made to allow space in tt to accommodate the nul-terminating character, the code functions well in making conversions to military time. By initializing tt to zero all elements during declaration/definition, you have insure tt will be nul-terminated when AM or PM are added. e.g.
#include <stdio.h>
#include <string.h>
int main (void) {
int hh, mm, ss;
char tt[3] = "";
printf (" enter time in HH:MM:SS AM/PM: ");
if (scanf ("%d:%d:%d %[^n]%*c", &hh, &mm, &ss, tt) != 4) {
fprintf (stderr, "error: invalid read of time.n");
}
hh = (strcmp (tt, "PM") == 0 && hh != 12) ? hh + 12 : hh;
if (strcmp (tt, "AM") == 0 && hh == 12) hh = 0;
printf (" %02d:%02d:%02dnn", hh, mm, ss);
return 0;
}
Example Use/Output
$ ./bin/tmread
enter time in HH:MM:SS AM/PM: 11:59:04 PM
23:59:04
Look it over and let me know if you have any questions.
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
Agreed, it can always be replaced with"%[^n]%*c"which is probably the better solution. It was originally left as%ssince we were dealing withAM,PMin a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...
– David C. Rankin
Apr 14 '16 at 16:11
add a comment |
With the changes made to allow space in tt to accommodate the nul-terminating character, the code functions well in making conversions to military time. By initializing tt to zero all elements during declaration/definition, you have insure tt will be nul-terminated when AM or PM are added. e.g.
#include <stdio.h>
#include <string.h>
int main (void) {
int hh, mm, ss;
char tt[3] = "";
printf (" enter time in HH:MM:SS AM/PM: ");
if (scanf ("%d:%d:%d %[^n]%*c", &hh, &mm, &ss, tt) != 4) {
fprintf (stderr, "error: invalid read of time.n");
}
hh = (strcmp (tt, "PM") == 0 && hh != 12) ? hh + 12 : hh;
if (strcmp (tt, "AM") == 0 && hh == 12) hh = 0;
printf (" %02d:%02d:%02dnn", hh, mm, ss);
return 0;
}
Example Use/Output
$ ./bin/tmread
enter time in HH:MM:SS AM/PM: 11:59:04 PM
23:59:04
Look it over and let me know if you have any questions.
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
With the changes made to allow space in tt to accommodate the nul-terminating character, the code functions well in making conversions to military time. By initializing tt to zero all elements during declaration/definition, you have insure tt will be nul-terminated when AM or PM are added. e.g.
#include <stdio.h>
#include <string.h>
int main (void) {
int hh, mm, ss;
char tt[3] = "";
printf (" enter time in HH:MM:SS AM/PM: ");
if (scanf ("%d:%d:%d %[^n]%*c", &hh, &mm, &ss, tt) != 4) {
fprintf (stderr, "error: invalid read of time.n");
}
hh = (strcmp (tt, "PM") == 0 && hh != 12) ? hh + 12 : hh;
if (strcmp (tt, "AM") == 0 && hh == 12) hh = 0;
printf (" %02d:%02d:%02dnn", hh, mm, ss);
return 0;
}
Example Use/Output
$ ./bin/tmread
enter time in HH:MM:SS AM/PM: 11:59:04 PM
23:59:04
Look it over and let me know if you have any questions.
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
edited Apr 14 '16 at 16:12
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
answered Apr 13 '16 at 8:08
David C. RankinDavid C. Rankin
43.3k33151
43.3k33151
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
Agreed, it can always be replaced with"%[^n]%*c"which is probably the better solution. It was originally left as%ssince we were dealing withAM,PMin a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...
– David C. Rankin
Apr 14 '16 at 16:11
add a comment |
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
Agreed, it can always be replaced with"%[^n]%*c"which is probably the better solution. It was originally left as%ssince we were dealing withAM,PMin a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...
– David C. Rankin
Apr 14 '16 at 16:11
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
scanf with "%s" is dangerous, since it does not limit the string length. See here msdn.microsoft.com/en-us/library/xdb9w69d.aspx or other places for how to avoid this problem in general.
– Stian Skjelstad
Apr 14 '16 at 10:50
Agreed, it can always be replaced with
"%[^n]%*c" which is probably the better solution. It was originally left as %s since we were dealing with AM, PM in a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...– David C. Rankin
Apr 14 '16 at 16:11
Agreed, it can always be replaced with
"%[^n]%*c" which is probably the better solution. It was originally left as %s since we were dealing with AM, PM in a fixed format file, it avoided having to discuss the use of the assignment suppression operator, etc...– David C. Rankin
Apr 14 '16 at 16:11
add a comment |
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3
You are 1-char short on
char tt[2];You forgot about the nul-terminating character. You need at minimumchar tt[3] = "";to holdAMorPM(the initialization is just good practice)– David C. Rankin
Apr 12 '16 at 10:32
@DavidC.Rankin, how does variable hh return zero, just because of char pointer is having a shorter storage space? and how does it run on hackerrank?
– cs1193
Apr 12 '16 at 10:35
3
It runs poorly. You invoke undefined behavior.
– Lundin
Apr 12 '16 at 10:41
2
@cs1193 It depends on the layout of variables on the stack. If
ttis right beforehh, the final nul character will overwrite the first byte ofhh, setting it to zero on a little endian architecture.– nwellnhof
Apr 12 '16 at 11:01