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int x = 5, y = 10;
if(x > 0)
y = y + 100;
else;
y = y + 200;
cout << "y = " << y << endl;
The output: 310
I know that whenever there is a semicolon after else it is treated as there is nothing. I also know that if there were no curl braces then we only execute the first statement after if.
Then why the answer here appears as the second statement was executed?
Also, if the else was not there will the second be executed also and why?
After an if and after an else there needs to be exactly one statement. The statement after if will be executed if the condition is true, the statement after else will be executed if the condition is false.
Now the important thing to understand is the following:
A single semicolon ; is a statement. It's an empty statement and putting it behind if or behind else fullfils the requirements of a statement.
A block between curly brackets {} is a statement. It groups multiple statements together, but it is one statement and thus also fulfills the requirements.
Any other statement that comes after the first statement after if or else has nothing to do with the if or else and will be executed like any other code would.
So to break down your example:
if(x > 0)
y = y + 100;
else;
y = y + 200;
is equivalent to:
if(x > 0)
y = y + 100; // first statement after if
else
; // first statement after else
y = y + 200; // separate statement uneffected by if or else
Removing the else gives us this:
if(x > 0)
y = y + 100; // first statement after if
y = y + 200; // separate statement uneffected by if
and of course the statement y = y + 200; will be executed, because it has nothing to do with the if or the else.
In this case, both statements will be executed.
if(x>0)
is true so the first part will work
y = 110
after this, then we reach else and that is the end of the line the next line does not have anything to do with the if-else block, it will always execute. hence
y = 110 + 200
, so y will have a final value of 310.
Hope this helps, cheers.
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for (unsigned int i = 0; i < list.size(); i++) {
if (list.at(i) = n) {
cout << "True";
return 0;
}}
I was wondering why this would not work I understand that tou should use list.at(i) == n.
However i thought that a single = means assigning, and a double == means equal to. I understand it is different but wouldn't using only one = still be correct when using it in an if statement?
It would not necessarily be correct. When you use an assignment expression as a boolean for integers, it will return true if the integer is not zero, and it will return false if the integer is zero.
Suppose our list looks like this: 1, 2, 0, 5. Now, suppose we have this if-statement:
if (list.at(0) = 1) {
cout << "True";
}
Since the 1 in list.at(0) = 1 is not 0, the if-condition will be satisfied. If we used ==, it would be satisfied since the first value is indeed 1.
Now let's suppose we have this if-statement:
if (list.at(1) = 3) {
cout << "True";
}
The "True" would be printed because 3 is not equal to 0. However, if we replaced = with ==, the "True" would not be printed since the second value is not 3.
Let's look at one last example.
if (list.at(2) = 0) {
cout << "True";
}
This would not print out "True" since we are assigning list.at(2) to 0. However, if we replaced the = with ==, the "True" would be printed since the third value in the list is actually 0.
This shows that = cannot be used as ==.
P.S. And, if you wanted to use the list later, your list would be modified into a different list.
if (condition) {
// block of code to be executed if the condition is true
}
Here is your code list.at(i) = n is an assignment and not a condition. Seeing your code I can say that you want to check if any value in the list is equal to n or not if it is then you want to print True.
So to do this you have to use a condition if(list.at(i)==n).
For more information read about condition statements, comparison operators, and assignment operators.
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I keep getting this error "Control may reach end of non-void function". Can anyone help me get through? I am stuck here. Thank you.
bool Vector_double::erase(int ind1, int ind2){
if(ind1 >= count || ind2 >= count || ind1 >= ind2){
if(ind1 == ind2){
erase(ind1);
return true;
}
return false;
}
else{
double *narr = new double[count - ind2 - 1];
for(int i = ind2 + 1; i < count; ++i){
narr[i - ind2 - 1] = arr[i];
}
for(int i = ind1; i < ind1 + count - ind2 - 1;++i){
arr[i] = narr[i - ind1];
}
count = count - (ind2 - ind1) - 1;
}
}
Your function promises to return something (bool). However, the code contains paths that don't return anything. In order to fix this bug, start by documenting (in plain English) what the returned value is supposed to express. Then, adjust your code.
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I have a task to make a code which will write 100 first numbers of an equation (or a function, I don't know what this is)
A(n) = (A(n-1))^2 -n*A(n-2) where A(1) = 1 and A(2) = 1
It has to be solved recursively. I have written this code so far
#include <iostream>
using namespace std;
int rekurzija(int n){
if(n=1){
return 1;
}
if(n=2){
return 1;
}
if(n>2){
return rekurzija(n-1)*rekurzija(n-1)-n*rekurzija(n-2);
}
}
int main(){
for(int n=1;n<101;n=n+1){
cout << rekurzija(n) << endl;
}
}
The problem is that the program returns 1 hundred times instead of 1,1,-2,0,...(instead of actually solving this function). What is wrong in this code?
You are using simple assignment operator = instead of Is equals to relational operator == in your rekurzija() function for if conditions
if(n = 1) //here `n = 1`is an assignment statement
{
//something...
}
What happens if you use = instead of ==?
The if condition will always evaluate to be true if the assigned value in the assignment statement is non-zero number.
Note: An assignment to zero evaluates to be false i.e, for if(n = 0), the if block will not be entered. You don't have any such if blocks in your code.
So your first if is always evaluated to be true because you are assigning a non-zero value i.e, 1 and thus your function always returns 1. that's the reason why you get 100 1's as your answer.
So, instead try changing all the if conditions to something like:
if(n == 1)
{
//something...
}
This would check if n is equals to 1 or not. If n is equal to 1 then the if block is entered, else it would not enter the if block and the next if condition is checked.
Note: Just remember this while using the = and == operators
= is for assignment
== is for comparison
When you compare things in C++ you need to do it like:
if (a == b)
and not
if (a = b)
The latter will assign b to a and return the value of a.
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I'm trying to generate and print out 5 numbers from 1 to 5, but not in sequence. I'm using a self-written function, 'appearBefore' that will check whether the number has appeared before.
The function appearBefore will return '0' if the number has not appeared before, and '1' if the function has appeared before.
At the moment, the do-while loop doesn't get out of the loop even when 0 is returned. The program never ends. Any recommendations on what I can do?
EDITS - The downvotes sure comes fast. I have added the counter++, but it still does not work. Perhaps someone can advice on the inner-loop?
while (count < 5) {
repeat = 1;
do {
randomNumber = rand() % 4 + 1;
cout << randomNumber;
repeat = appearBefore(randomNumber);
cout << " " << repeat << endl;
} while (repeat == 1);
//Add the number into an array of numbers that have appeared before
checker[counterForChecker] = randomNumber;
counterForChecker++;
counter++;
}
This is the function appearBefore (the variables are global variables):
int appearBefore(int number) {
int x = 0;
int match = 0;
while (x < counterForChecker+1) {
if (checker[x] == number) {
match = 1;
break;
}
else {
match = 0;
}
x++;
}
return match;
}
You check for count < 5 while increasing counterForChecker.
Set the while condition to
while (counterForChecker < 5)
or increase the counter
counter++; // counterForChecker++;
(Assuming that counter++; actually says count++;...)
If x and k are positive, x % k is a number between 0 and k - 1.
So you have four possible values to choose from (1,2,3,4), and you're looping until you've found five unique values.
That will never end well.
To generate numbers from 1 to 5, use rand() % 5 + 1;
You'll want to change the variable count. This is now not done, so since the value does not change the loop will not end.
The loop is running while count < 5 and you never increment count.
Did you mean to use:
while (counterForChecker < 5)
If not, add:
++count;
at the end of the while loop
Use a debugger and step through the code, looking at the values of the variables as you do so. You'll learn more about how everything is working.
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What is the difference between this:
s = 0;
if (x > 0) s++;
if (y > 0) s++;
and this:
s = 0;
if (x > 0) s++;
else if (y > 0) s++;
Any help would be greatly appreciated.
When you write else if instead of if, program will not check the else if statement if x > 0, but when you write two if statements program will check both conditions, no matter if x > 0 or not.
In the first case the both conditions are checked because there are two different if statements.
In the second case the second condition is checked only if the first condition is evaluated to false.
Say x is 10 and y is 10. At the end of the first set of statements, s will be equal to 2. At the end of the second set of statements, s will be equal to 1.
The second example
s = 0;
if (x > 0) s++;
else if (y > 0) s++;`
will check for the y value only if x > 0 is false. The first example will execute the check regardless of x's value.