I am writing two functions in a program to check if a string has an assigned numeric code to its structure array or if the given numeric code has an assigned string in the same structure array. Basically, if I only know one of the two, I can get the other. I wrote the following:
int PrimaryIndex::check_title_pos(std::string title) {
bool findPos = true;
if (findPos) {
for (int s = 1; s <= 25; s++) {
if (my_list[s].title == title) {
return s;
}
}
} else {
return -1;
}
}
std::string PrimaryIndex::check_title_at_pos(int pos) {
bool findTitle = true;
if (findTitle) {
for (int p = 1; p <= 25; p++) {
if (my_list[p].tag == pos) {
return my_list[p].title;
}
}
} else {
return "No title retrievable from " + pos;
}
}
However, it says not all control paths have a return value. I thought the else {} statement would handle that but it's not. Likewise, I added default "return -1;" and "return "";" to the appropriate functions handling int and string, respectively. That just caused it to error out.
Any idea on how I can keep this code, as I'd like to think it works but cant test it, while giving my compiler happiness? I realize through other searches that it sees conditions that could otherwise end in no returning values but theoretically, if I am right, it should work fine. :|
Thanks
In the below snippet, if s iterates to 26 without the inner if ever evaluating to true then a return statement is never reached.
if (findPos) {
for (int s = 1; s <= 25; s++) {
if (my_list[s].title == title) {
return s;
}
}
}
Related
I was wondering what I may have done wrong in writing this simple function which is supposed to return true if the given number is a prime, or false if not a prime.
bool isPrime(int num)
{
if (num <= 1)
{
status = false;
}
else
{
for (int i = 1; i <= num; i++)
{
if (num % i == 0)
{
dividers++;
}
}
if (dividers == 2)
{
status = true;
}
else
{
status = false;
}
}
return status;
}
Obviously, my main looks like this:
bool isPrime(int num);
bool status;
int dividers = 0;
int main() {
isPrime(2);
if (!isPrime)
{
std::cout << "Not prime" << std::endl;
}
else
{
std::cout << "Prime" << std::endl;
}
return 0;
}
I'm a C++ beginner and I'd really appreciate it if someone could help me there and correct my logic.
Have a good day:)
The immediate problem is in this two lines:
isPrime(2);
if (!isPrime)
The first line calls the function and discards the returned value. The second line converts a pointer to the function to bool. The output of your code does not depend on what you actually do in isPrime.
That is not how you call a function and use its result!
Instead you want
if (isPrime(2)) {
or
bool isP = isPrime(2);
if (isP) { ...
As mentioned in comments, there are also problems in the implementation of isPrime, but I hope this is enough to set you back on the right track.
PS: You should get rid of the global variable status. You do not need both, the return value and a global that stores the result, and if you can choose, you should definitely go for the return value.
First of all sorry for too much code
Here there is a vector (teamNum) with type class, the class contain a vector (player) with type struct, it is a little complicated, but here in this function I need to check if there is a player in teamNum which contain tName equal to _tname (function parameter) contain (the player) pID equal to _pID (function parameter)
bool thereIsSimilarID(string _tname, int _pID)
{
for (int i = 0; i < teamNum.size(); i++)
{
if (teamNum[i].tName == _tname)
{
for (int j = 0; j < teamNum[i].player.size(); j++)
{
if (teamNum[i].player[j].pID == _pID)
return true;
}
}
else if (i == (teamNum.size() - 1))
{
return false;
}
}
}
And in the main
int main()
{
cout << "\n" << thereIsSimilarID("Leverpool", 1) << endl;
}
The output is 24 !!!!!
(good note that this happen just when the team (Leverpool) is the last team in the vector teamNum)
Again sorry for too much code but I need to know the bug not only fix the problem I need to learn from you
You encountered undefined behaviour.
If you take the if (teamNum[i].tName == _tname)-branch on the last element, but find no player with the correct pID, you don't return anything. Which means, that the return value is whatever random value is currently in the memory location that should hold the return value. In your case it happens to 24. But theoretically, everything could happen.
The same problem occurs when teamNum is empty.
The solution is to make sure to always return a value from a function (except if it has return type void of course):
bool thereIsSimilarID(string _tname, int _pID)
{
for (int i = 0; i < teamNum.size(); i++)
{
// In this loop return true if you find a matching element
}
// If no matching element was found we reach this point and make sure to return a value
return false;
}
You should take a look at your compiler settings and enable all the warnings. And often it's good to let it treat certain warnings as errors.
I am new to programming and have an exercise in which I create a function to check whether an array of type char hold particular values.
Here is my function:
bool arrCheck(char n[],char pos1,char pos2,char pos3,int size)
{
int n1,n2,n3;
for (int i=0;i<size;i++)
{
if (n[i]==pos1)
{
n1=1;
}
if (n[i]==pos2)
{
n2=1;
}
if (n[i]==pos3)
{
n3=1;
}
}
if ((n1==1)&&(n2==1)&&(n3==1))
{
return true;
}
}
here is my test program:
int main()
{
char a[5]={'6','1','a','a','a'};
if (arrCheck(a,'1','6','9',5))
{
cout<<"true\n";
}
}
I thought the result is supposed to be false but all I got is true. What did I do wrong?
n1, n2 and n3 are default-initialized and they have indeterminate values at first. Initialize them before checking their values. Also do not forget to return something even when the condition is false.
Try this:
bool arrCheck(char n[],char pos1,char pos2,char pos3,int size)
{
int n1=0,n2=0,n3=0;
for (int i=0;i<size;i++)
{
if (n[i]==pos1)
{
n1=1;
}
if (n[i]==pos2)
{
n2=1;
}
if (n[i]==pos3)
{
n3=1;
}
}
return (n1==1)&&(n2==1)&&(n3==1);
}
Using boolto store boolean values and using const to mark that the contents of array won't be changed may be better .
bool arrCheck(const char n[],char pos1,char pos2,char pos3,int size)
{
bool n1=false,n2=false,n3=false;
for (int i=0;i<size;i++)
{
n1=n1||(n[i]==pos1);
n2=n2||(n[i]==pos2);
n3=n3||(n[i]==pos3);
}
return n1&&n2&&n3;
}
1) Use a bool variable instead of three int variable
2) Initialize it (You have not initialized the int variable and they have random garbage value)
3) Also add else condition to return false value (Your code is not returning false).
4)Also print false in main function using else condition.
Hope this helps you..!
THE CODE IS ALRIGHT. You just forgot to add some statements and this is causing the error (it might or might not have been silly on your part).
Your definition of the function arrCheck() is incomplete. It returns true if a certain condition is fulfilled but what if it isn't? In that case, you must return false. But in your code, false is never returned. So firstly, you've gotta add an else statement after the last if statement in the arrCheck() method to this:
if((n1==1)&&(n2==1)&&(n3==1)){
return true;
}
else{
return false; //this has to be added
}
It can now return false if such a case is encountered.
Also, you must display "false" in the main method if arrCheck() returns false. You are recommended to add an else statement after the if statement in the main() method. See the modification below:
if (arrCheck(a,'1','6','9',5))
{
cout<<"true\n";
}
else{
cout<<"false\n"; //it must show false;
}
Once you correct these, your code will produce the correct output.
P.S. This answer serves as an elaboration of the answer earlier submitted by #KUSHAGRA GUPTA.
int n1,n2,n3;
This line leads to undefined behaviour because you do not initialise the variables yet attempt to read from them later on even if not all of them have been assigned a value:
if ((n1==1)&&(n2==1)&&(n3==1))
Fix the undefined behaviour by initialising the variables to 0:
int n1 = 0;
int n2 = 0;
int n3 = 0;
There is another case of undefined behaviour when your function does not state what to return if the condition is not true. Fix this, too:
if ((n1==1)&&(n2==1)&&(n3==1))
{
return true;
}
else
{
return false;
}
Or simply:
return (n1==1)&&(n2==1)&&(n3==1);
change that line to like this.int n1= 0,n2= 0,n3 = 0;
because when uninitialized these variable have garbage values.
bool arrCheck(char n[],char pos1,char pos2,char pos3,int size)
{
int first = 0,second = 0, third = 0;
for (int i=0;i<size;i++) {
if (n[i]==pos1) {
first = 1;
} else if (n[i]==pos2) {
second = 1;
} else if (n[i]==pos3) {
third = 1;
}
}
if( first+ second + third == 3)
return true;
else
return false;
}
I'm trying to make function that has a loop that checks every member of an array made from boolean variables and exits when it finds the first "true" value.
That's what I have now:
bool solids[50];
int a,i;
//"equality" is a function that checks the equality between "a" and a defined value
solids[0] = equality(a,&value_1);
solids[1] = equality(a,&value_1);
solids[2] = equality(a,&value_1);
solids[3] = equality(a,&value_1);
for (i = 0; solids[i] != true; i++)
{
[...]
}
But I have no idea, what should I put into the loop?
My attempt was
for (i = 0; i <= 50; i++)
{
if (solids[i] == true)
{
return true;
break;
} else {
return false;
}
}
,that should return true after the first found true and return false if the array has no member with true value, but it doesn't seem to work in the code.
Is it wrong? If yes, what is the problem?
PS.: I may count the number of trues with a counter but that's not an optimal solve to the problem, since I just look for the FIRST true value and consequently, the program doesn't have to check all the 50 members. Needley to count, how many unnecesary steps should this solve would mean.
here's a short example usage of std::find() as advised by #chris:
bool find_element_in_array() {
bool solids[50];
int length;
/* ... do many operations, and keep length as the size of values inserted in solids */
bool* location = std::find(solids, length, true);
// if element is found return true
if (location != solids + length)
return true;
// else return false
return false;
}
Once you have solids correctly set (it looks like you're currently setting every value to the same thing), you can make a loop that exits on the first true like this:
for (i = 0; i < 50; i++)
{
if (solids[i] == true)
{
return true;
}
}
return false;
I'd also just move the declaration of i into the for loop body, since it's not used outside, but the above answers your question.
return immediately exits the function, so there is no need to break the loop after.
If it's sufficient to exit the function right after the search, you should write something like:
for (int i = 0; i < 50; i++) {
if (solids[i]) return true;
}
return false;
If you need to use the result of the search in the same function, use additional variable:
bool found = false;
for (int = 0; i < 50; i++) {
if (solids[i]) {
bool = true;
break;
}
}
if (found) { ...
my assignment requires me to write a function that reads in a title and return the corresponding fee to the calling function. if the title is not in the list, return -1.0.
this is what i have got at the moment:
struct eventType
{
string title;
double fees;
};
eventType eventTable[10];
int findFees (string newTitle, string newFees)
{
int Index = 0;
int flag;
while (Index < 9) && (eventTable[Index].title != newTitle))
Index = Index + 1;
if (eventTable[Index].title == newTitle)
{
eventTable[Index].fees = newFees;
flag = 0;
}
else
flag = -1;
return flag;
}
is anything missing?
update
after looking at the advice u guys have given, i have adopted and changed the codes to:
double findFees (string title)
{
for (int Index = 0 ; Index < 10 ; Index++)
{
if (eventTable[Index].title == title)
{
return eventTable[Index].fees;
}
}
return -1.0;
}
I'm not sure if this is correct either but I do not need a new title or new fees since these values are to be found within eventTable, and return it.
corrections?
I don't want to give away the answer for you, but here are two things you should keep in mind:
When you have a conditional or a loop, you need to surround statements in { and } so that the compiler knows which statements go inside the loop.
Second, C++ is a type-safe language, meaning that if you are assigning variables to a value of a different type, your program won't compile, look through your code and see if you can find anything wrong on that front
It should be:
while (Index < 10)
And you said it should return the fee, but it returns 0 when found. (This is ok, since you are passing in the fee, why return it too?)
I would also change the signature of the function to be:
int findFees (const string &newTitle, const string &newFees)
and while you are at it, have it return a "bool" instead of a flag to denote success since:
if(findFees(blahTitle, blahFees))
sounds a lot better than:
if(findFees(blahTitle, blahFees) == 0)
when checking for whether the title is found.
It seems to me your function does not return the fees, as you described.
It looks like it updates the eventTable, changing the fee stored there, and returns a flag if the update was done successfully.
Please clarify. Do you want to find the fee stored in the eventTable and return it? Or do you want to update the eventTable with new data? Or a hybrid of both.
Still, for a noob, your code is well structured and reasonably well written.
You could simplfy it as so.
int flag = -1;
int Index = 0;
while(Index <= 9)
{
if(eventTable[Index].title == newTitle)
{
eventTable[Index].fees = newFees;
flag = 0
break;
}
}
return flag;
eventTable[Index].fees = newFees;
This won't work because fees is a double and newFees is a string. Also you didn't say anything about changing the fees, so I'm confused by that line.
If you want to return the fees of the item you found, you should just put return eventTable[Index].fees; at that point and change the return value of the function to float.
Your description (return the fee, or -1.0 if not found) does not match your code:
struct eventType
{
string title;
double fees;
};
eventType eventTable[10];
double findFees (string newTitle)
{
for (int Index = 0 ; Index < 10 ; Index++)
{
if (eventTable[Index].title == newTitle)
{
return eventTable[Index].fees;
}
}
return -1.0;
}
The only error I see is
while (Index < 9) && (eventTable[Index].title != newTitle))
should probably be:
while ((Index < 10) && (eventTable[Index].title != newTitle))
Note the missing '('. Otherwise you miss matching the last entry in the array.
I would probably write the function something like:
double findFees (const string& title, double newFee)
{
for (int i = 0; i < 10; i++)
{
if (eventTable[i].title == title)
{
eventTable[i].fees = newFee;
return newFee;
}
}
return -1.0;
}
This way you will not iterate through the entire array if you already found the item you where searching for.