I'm doing a scrolling menu, this is the code of my scrolling menu:
vector<string> menuVector;
int _tmain(int argc, _TCHAR* argv[]){
menuVector.push_back("Login");
menuVector.push_back("Exit");
scrollingMenu_();
cin.get();
return 0;
}
void scrollingMenu_(){
ShowConsoleCursor(false);
int pointer = 0;
while (true){
system("cls");
SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 15);
welcome();
for (int i = 0; i < menuVector.size(); ++i){
if (i == pointer){
SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 8);
cout << "\t\t\t\t\t\t> " << center(menuVector[i], 5) << " <" << endl;
}
else{
SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 15);
cout << "\t\t\t\t\t\t " << center(menuVector[i], 5) << " " << endl;
}
}
while (true){
if (GetAsyncKeyState(VK_UP) != 0){
pointer -= 1;
//if menu option selected is before the first option, it will back to the last menu option
if (pointer == -1){
pointer = menuVector.size() - 1;
}
break;
}
else if (GetAsyncKeyState(VK_DOWN) != 0){
pointer += 1;
//if menu option selected is after the last option, it will back to the first menu option
if (pointer == menuVector.size()){
pointer = 0;
}
break;
}
else if (GetAsyncKeyState(VK_RETURN) != 0){
switch (pointer){ //this is the switch case
case 0:
cout << "\n\n\nStarting new game...";
Sleep(1000);
break;
case 1:
exit(0);
break;
}
break;
}
}
Sleep(150);
}
}
As for the case switch inside my scrollingMenu_() function, the switch case will not be the same sometime I called the function, is there something like scrollingMenu_(switchcase), so by that time when I'm calling the function then I can define what my switchcase will do. Otherwise I have to copy paste the same scrollingMenu() function code for the parts that I need to do a menu with different menu options, which looks kinda redundant. I tried to research it online, but I didn't know how to search so I didn't get what I want.
Thank you.
If I understand you correctly, you want to be able to have different "menus" in your vector, and therefore be able to do different things in the switch depending on what menu is currently "active"?
Then I suggest a completely different design. Instead of a vector of strings for the menu, and a switch statement to select between the behaviors, use two vectors: One for the menu text (like you already have), and one for the menu "actions".
Then instead of using a switch to select between the actions for a menu alternative, simply use the pointer as an index into the second vector to call the action.
You can do this quite easily with std::function in combination with std::bind or lambda expressions.
For the menu you currently have it would be something like
std::vector<std::function<void()>> actionVector;
// ...
// Set up the menu vectors for the current menu
menuVector = {
"Login",
"Exit"
};
actionVector = {
[]() { cout << "\n\n\nStarting new game..."; Sleep(1000); },
[]() { std::exit(0); }
};
scrollingMenu_();
// ...
else if (GetAsyncKeyState(VK_RETURN) != 0){
actionVector[pointer](); // Call the action
}
Say we have the following if-statement:
if (arg.compare("abc") == 0)
{
...
}
If I want to convert it to have a switch form, is the following correct?
switch (arg)
{
case "arg.compare("abc") == 0: cout<<"statements the same";
break;
}
Thanks.
If ever the following switch statement was possible:
switch (arg)
{
case arg.compare("abc1") == 0: cout << "statements the same1";
break;
case arg.compare("abc2") == 0: cout << "statements the same2";
break;
}
It would be totally equal to the following if statement (do you want a break statement?):
if(arg.compare("abc1") == 0) cout << "statements the same1";
// no break is needed
else if(arg.compare("abc2") == 0) cout << "statements the same2";
// no break is needed
Which is really equal to:
if(arg.compare("abc1") == 0)
{
cout << "statements the same1";
}
else if(arg.compare("abc2") == 0)
{
cout << "statements the same2";
}
And it is how if-else statement works exactly the way that you wanted, because it will not check for the next conditions if one of them is true.
If the set of strings is statically known to you (at development time, e.g. because it is a set of known keywords or identifiers) you might want to use a perfect hash generator like gperf
If coding in C++11 you could also make a map of anonymous functions:
std::map<std::string, std::function<void(const std::string&)>
funmap = {
{ "abc", [&](const std::string& name)
{ std::cout << name; } },
{ "cde", [&](const std::string& name)
{ do_something_with(name); } },
};
later you would do something like
auto it = funmap.find(somestring);
if (it != funmap.end()) it->second(somestring);
char x;
bool tf;
void IsNumber(char x)
{
switch (x)
{
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
case '0':
bool tf(true);
break;
default:
bool tf(false);
break;
}
}
int main(int argc, const char * argv[])
{
using namespace std;
cout << "Test if a character is a number: " << endl;
char x;
cin >> x;
IsNumber((char) x);
if (bool tf = true)
cout << "True" << endl;
if (bool tf = false)
cout << "False" << endl;
return 0;
}
I am getting an error after the default: saying I can't redefine the variable. Also, it says, at the bottom, that I the variable tf isn't a variable. I am really new to C++, I only know python can someone help me out?
New code giving me an error:
#include <iostream>
bool tf;
tf = true;
bool IsNumber(char x)
{
switch (x)
{
case '1':
You're trying to declare two variables with the same name in the same scope. The switch statement itself defines a scope, but each case clause does not. If you want a scope within a case clause, then you'll have to provide one yourself:
case '0':
{
bool tf(true);
break;
}
Although it's not clear what good that is; you're declaring a local variable then ignoring it. Perhaps you meant to set the global variable:
case '0':
tf = true;
break;
so you could then check it with
if (tf) // NOT if (bool tf = true) - that also declares a new local variable
or, less freakily, perhaps you want to return a value:
bool IsNumber(char x) {
switch (x) {
case '0':
// and so on
return true;
default:
return false;
}
}
and test it with
if (IsNumber(x)) {
cout << "True" << endl;
} else {
cout << "False" << endl;
}
or, if verbosity isn't your thing
cout << (IsNumber(x) ? "True" : "False") << endl;
or even
cout << boolalpha << IsNumber(x) << endl;
You should probably take some time to read an introductory book until you're comfortable with the basics such as scopes, declarations and definitions. Here are some recommendations.
You haven't assigned anything to tf, for comparison operators we want =='s instead of just the ='s.
if (tf == true) {
}
You can only define a variable one you can assign it as many times as you need.
bool tf = false
means I am define a variable and assigning it
if I just want to assign it later
tf = false
if I want to do a conditional test
if (tf){do stuff}
You have x defined at the very top as a global variable, and then try and define it again in main. You have to pick one or the other, or rename one. What you probably want to do is get rid of the one in main.
You also have your bools compared as = instead of how they should be like ==.
Edit: You actually don't need the comparison in there at all.
if(tf){
cout << "True\n"
}
else cout << "False\n"
That will see if tf is true and output true and if not, output false.
This is a growing source of irritation for me at the moment, when I press the corresponding button for the cases (they're initialized above) they don't actually execute and I'm stuck in the menu.
I'm sure this is ridiculously simple and I'm just not seeing it.
Edit: Added more, upon request
const int POKER = 1;
const int EVAL = 2;
const int EXIT = 3;
const char FIVE_CARD = 'a';
const char TEXAS = 'b';
const char OMAHA = 'c';
const char SEVEN_CARD = 'd';
const char GO_BACK = 'e';
const char MENU[] = "\nPlease choose an option from the following:\n"
"1) Play Poker\n2) Set Evaluation Method\n3) Quit\n: ";
const char POKER_MENU[] = "\nPlease choose your game:\n"
"a) 5 Card Draw\nb) Texas Hold 'Em\nc) Omaha High\n"
"d) 7 Card Stud\ne) Go back\n: ";
int main()
{
int choice = 0;
char poker_choice;
do
{
choice = askForInt(MENU, EXIT, POKER);
switch(choice)
{
case POKER :
do
{
choice = askForChar(POKER_MENU, GO_BACK, FIVE_CARD);
switch(poker_choice)
{
case FIVE_CARD :
std::cout << "Not implemented yet" << std::endl;
break;
case TEXAS :
std::cout << "Not implemented yet" << std::endl;
break;
case OMAHA :
std::cout << "Not implemented yet" << std::endl;
break;
case SEVEN_CARD :
std::cout << "Not implemented yet" << std::endl;
break;
case GO_BACK :
break;
}
}while(poker_choice != GO_BACK);
case EVAL :
std::cout << "Not implemented yet" << std::endl;
break;
case EXIT :
break;
}
}while(choice != EXIT);
choice = askForChar(POKER_MENU, GO_BACK, FIVE_CARD);
should be
poker_choice = askForChar(POKER_MENU, GO_BACK, FIVE_CARD);
Since you mentioned this is inside a method,
There are few things to check here;
Once inside the method, just print poker_choice and see if your the value is getting passed correctly.
Check if all the cases FIVE_CARD, TEXAS are declared as constants of the same data type.
Your error seems to be on this line:
choice = askForChar(POKER_MENU, GO_BACK, FIVE_CARD);
You test poker_choice in your switch but you assign the value to choice.
It should be:
poker_choice = askForChar(POKER_MENU, GO_BACK, FIVE_CARD);
// ^^^^^^
switch(poker_choice)
// ...
When I try to compile I get this error:
1>------ Build started: Project: snake, Configuration: Debug Win32 ------
1> exercise.cpp
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(13): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(16): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(19): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(22): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(25): error C2059: syntax error : '>'
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(28): error C2059: syntax error : '=='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(34): warning C4065: switch statement contains 'default' but no 'case' labels
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Code:
#include <iostream>
using namespace std;
int main(){
int score;
//Vraag de score
cout << "Score:";
cin >> score;
//Switch
switch(score){
case >= 100:
cout << "a";
break;
case >= 50:
cout << "b";
break;
case >= 25:
cout << "c";
break;
case >= 10:
cout << "d";
break;
case > 0:
cout << "e";
break;
case == 0:
cout << "f";
break;
default:
cout << "BAD VALUE";
break;
}
cout << endl;
return 0;
}
How can I fix this problem? It's a console application, Win32 and my IDE is Windows Enterprise C++ 2010.
I'm learning from Beginning C++ Through Game Programming.
Some compilers support case ranges like case x ... y as an extension to the C++ language.
Example:
#include <iostream>
using namespace std;
int main(){
int score;
//Vraag de score
cout << "Score:";
cin >> score;
//Switch
switch(score){
case 0:
cout << "a";
break;
case 0 ... 9:
cout << "b";
break;
case 11 ... 24:
cout << "c";
break;
case 25 ... 49:
cout << "d";
break;
case 50 ... 100:
cout << "e";
break;
default:
cout << "BAD VALUE";
break;
}
cout << endl;
return 0;
}
GCC 4.9, Clang 3.5.1 and Intel C/C++ Compiler 13.0.1 seem to support it (tried on http://gcc.godbolt.org/). On the other hand, Visual C++ 19 doesn't (tried on http://webcompiler.cloudapp.net/).
In C++ case labels are constant expressions, not expressions in general. You need a chain of if-then-else statements to do what you are trying to do.
Alternatively, you can enumerate the values in the switch. This runs marginally faster (though it does not matter in cases like yours), but it is considerably less readable:
switch(score) {
case 0: cout << "f"; break;
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10: cout << "e"; break;
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
case 18:
case 19:
case 20:
case 21:
case 22:
case 23:
case 24:
case 25: cout << "c"; break;
// ...and so on, you get the idea...
}
You can fix this problem by using a series of if/else if statements. Switch/case cannot be used like this in C++.
It can be done using a std::map with switch:
enum Interval {
One,
Two,
Three,
NotFound };
// [0,10[ is One, [10,30[ is Two, [30,55[ is Three
std::map<int,Interval> imap {
{ { 0, One },
{ 10, Two },
{ 30, Three },
{ 55, NotFound } };
Interval ivalue = NotFound;
auto f = imap.lower_bound( value );
if( f != imap.end() ) ivalue = f->second;
switch( ivalue ) {
case One : ...
case Two : ...
case Three : ...
default: ...
}
Switch-case is not a great option for testing ranges. The best option is to use several if :
if (score<0) cout << "BAD VALUE";
if (score == 0) cout << "f";
if (score>0 && score<10) cout << "e";
if (score>=10 && score <25) cout << "d";
if (score>=25 && score <50) cout << "c";
if (score>=50 && score <100) cout << "b";
If running time is an issue, the following solution is faster :
if (score == 0) cout << "f";
else if (score<10) cout << "e";
else if (score <25) cout << "d";
else if (score <50) cout << "c";
else if (score <100) cout << "b";
else if (score>=100) cout << "a";
else cout << "BAD VALUE";
There's a GCC extension that does exactly what you want.
In C++ a switch statement can only match constant integer values:
switch (i)
{
case 1:
//... stuff
break;
case 2:
//... stuff
break;
default:
//... stuff
}
The standard does not allow for this:
6.4.2 The switch statement [stmt.switch]
[...] Any statement within the switch statement can be labeled with one or more case labels as follows:
case constant-expression :
where the constant-expression shall be an integral constant expression (5.19).
In other words, you can only use case-values that expand into a single, integral, "hard" compile time constant (e.g. case 5+6:, enum {X = 3}; ... case X*X:).
The way around this is to use if-statements. E.g., to replace
switch (x)
case 0..100:
you'd instead
if (x>=0 && x<=100)
.
std::map::upper_bound + C++11 lambdas
https://stackoverflow.com/a/35460297/895245 mentioned lower_bound, but we can also get rid of the enum there with lambdas (or inheritance if you don't have it).
#include <functional>
#include <iostream>
#include <map>
int main() {
std::string ret;
const std::map<int,std::function<void()>> m{
{0, [&](){ ret = "too small"; }},
{2, [&](){ ret = "[0,2)"; }},
{5, [&](){ ret = "[2,5)"; }},
{7, [&](){ ret = "[5,7)"; }},
};
const auto end = m.end();
for (auto i = -1; i < 8; ++i) {
auto it = m.upper_bound(i);
if (it == end) {
ret = "too large";
} else {
it->second();
}
std::cout << i << " " << ret << std::endl;
}
}
Output:
-1 too small
0 [0,2)
1 [0,2)
2 [2,5)
3 [2,5)
4 [2,5)
5 [5,7)
6 [5,7)
7 too large
Usage inside methods with static
To use this pattern efficiently inside classes, initialize the lambda map statically, or else you pay n log(n) every time to build it from scratch.
Here we can get away with the {} initialization of a static method variable: Static variables in class methods , but we could also use the methods described at: static constructors in C++? I need to initialize private static objects
It was necessary to transform the lambda context capture [&] into an argument, or that would have been undefined: const static auto lambda used with capture by reference
Example that produces the same output as above:
#include <functional>
#include <iostream>
#include <map>
#include <string>
class RangeSwitch {
public:
void method(int x, std::string &ret) {
static const std::map<int,std::function<void(std::string&)>> m{
{0, [](std::string &ret){ ret = "too small"; }},
{2, [](std::string &ret){ ret = "[0,2)"; }},
{5, [](std::string &ret){ ret = "[2,5)"; }},
{7, [](std::string &ret){ ret = "[5,7)"; }},
};
static const auto end = m.end();
auto it = m.upper_bound(x);
if (it == end) {
ret = "too large";
} else {
it->second(ret);
}
}
};
int main() {
RangeSwitch rangeSwitch;
std::string ret;
for (auto i = -1; i < 8; ++i) {
rangeSwitch.method(i, ret);
std::cout << i << " " << ret << std::endl;
}
}
That's simply not how switch works. It only takes single values. You'll have to use if-elseif blocks
I had the same problem with a score based problem and while the " if/elseif "statements were good to use, for intervals i found that the best option (for me at least because i like how it looks and it's easier for me as a beginner to see my mistakes) is " 1 ... 10 ". but don't forget to use a space between the number and the dots or the program will think that your interval is a number and u will get an error "2 many decimal dots...". Hope it helps.
int score;
int main()
{
cout<<"Enter score"<<endl;
cin>>score;
switch(score){
case 100:
cout<<"Your score is Perfect"<<endl;
break;
case 90 ... 99:
cout<<"You got A"<<endl;
break;
case 80 ... 89:
cout<<"You got B"<<endl;
break;
case 70 ... 79:
cout<<"You got C"<<endl;
break;
case 60 ... 69:
cout<<"You got D"<<endl;
break;
case 50 ... 59:
cout<<"You got E"<<endl;
break;
case 0 ... 49:
cout<<"You got F"<<endl;}
}
Switch case statements are a substitute for long if statements that compare a variable to several "integral" values ("integral" values are simply values that can be expressed as an integer, such as the value of a char). The condition of a switch statement is a value. The case says that if it has the value of whatever is after that case then do whatever follows the colon. The break is used to break out of the case statements.
Therefore, you cannot use such conditional statements in case.
The selective structure: switch
This is what worked for me. dividing the mark by 10 and then setting case 10 and 9 to display an "A"(this will display a "A" for any value between 90-100. Then case 8 to display "B", then case 7 will display a "C" for the values from 70-79 and so on.
#include <iostream>
using namespace std;
main ()
{
int mark;
cout << "enter your mark: ";
cin >> mark;
switch (mark/10)
{
case 10: case 9: cout << "A"; break;
case 8: cout << "B"; break;
case 7: cout << "C"; break;
case 6: cout << "D"; break;
case 5: cout << "PASS"; break;
default: cout << "FAIL"; break;
}
}
You can do the following:
//summarize the range to one value
If score < 0
score = -1
switch(score){
case 1:
//...
break;
case 2:
//...
break;
case -1: //complete neg. range
//...
break;
//...
}
Something like this?
case 'A'..'Z' where a not in ['I','L','O']:
Unfortunately no compiler I know of implements that particular extension, though GCC has can do ranges as other answers pointed out. For portability you can cut and paste this DWTFYW licensed snippet. If you're using a custom enum you might resort to code generation to make something similar.
#define CASE_NUMBER \
case'0':case'1':case'2':case'3':case'4':\
case'5':case'6':case'7':case'8':case'9'
#define CASE_ALPHA_LOWER \
case'a':case'b':case'c':case'd':\
case'e':case'f':case'g':case'h':\
case'i':case'j':case'k':case'l':\
case'm':case'n':case'o':case'p':\
case'q':case'r':case's':case't':\
case'u':case'v':case'w':case'x':\
case'y':case'z'
#define CASE_ALPHA_UPPER \
case'A':case'B':case'C':case'D':\
case'E':case'F':case'G':case'H':\
case'I':case'J':case'K':case'L':\
case'M':case'N':case'O':case'P':\
case'Q':case'R':case'S':case'T':\
case'U':case'V':case'W':case'X':\
case'Y':case'Z'
#define CASE_ALPHA CASE_ALPHA_UPPER:CASE_ALPHA_LOWER
#define CASE_ALPHANUM CASE_ALPHA:CASE_NUMBER
If you access to GHCI such as the online version at https://ghc.io/ you might just generate what you need and paste that into a header e.g.
foldl (++) "" ["case" ++ show x ++ ":" | x <- ['A'..'Z'], not $ x `elem` ['I','L','O']]
Here's a way which I hope is expressive and simple to follow.
You may be surprised by how far gcc/clang etc can optimise the code it generates. I would expect it to be at least as efficient as a switch/case.
#include <iostream>
template<class Value>
struct switcher
{
constexpr switcher(Value const& value) : value_(value) {}
constexpr switcher(Value const& value, bool enabled) : value_(value), enabled(enabled) {}
template<class From, class To, class F>
constexpr auto in_range(From&& from, To&& to, F&& f)
{
if (enabled and (from <= value_ and value_ <= to))
{
f();
return switcher(value_, false);
}
else {
return *this;
}
};
template<class F>
constexpr auto otherwise(F&& f)
{
if (enabled)
f();
}
Value const& value_;
const bool enabled = true;
};
template<class Value>
constexpr auto decision(Value const& value)
{
return switcher<Value>(value);
}
void test(int x)
{
decision(x)
.in_range(0, 10, [&] { std::cout << x << " maps to option A\n"; })
.in_range(11, 20, [&] { std::cout << x << " maps to option B\n"; })
.otherwise([&] { std::cout << x << " is not covered\n"; });
}
int main(int argc, char **argv) {
test(5);
test(14);
test(22);
}
A potentially useful insight is that switch accepts an expression, so you can fold multiple input values down to one switch case. It's a big ugly, but for consideration:
switch (score / 10)
{
case 10:
cout << "a";
break;
case 9: case 8: case 7: case 6: case 5:
cout << "b";
break;
case 4: case 3:
cout << "c";
break;
case 2:
if (score >= 25)
{
cout << "c";
break;
}
// else fall through...
case 1:
cout << "d";
break;
case 0:
cout << (score > 0 ? "e" : "f");
break;
default:
cout << "BAD VALUE";
break;
}
Of course, you could have divided by 5 and had case 4: (for 20-24) vs case 5: (25-29) rather than an if inside case 2:, but /10 is arguably more intuitive.
I know this is an old questiion, but since switch statements are in fact wrappers around labels, I find goto may be of (good) use here.
int value = 40;
if (value < 10) {
std::cout << "value < 10" << std::endl;
goto end;
}
if (value < 50) {
std::cout << "value < 50" << std::endl;
goto end;
}
if (value > 30) {
std::cout << "value > 30" << std::endl;
goto end;
}
end:
// resume
This way, you can omit all the elses and keep it compact.
You ought to be careful when using goto though (in general).