if else statement in C++

chris85

Hi in a code i am writing i need to say that if numbers numbers (lets call them fx and fxx) are not equal to zero then it will perform the equation below.But if the if condition is not true (i.e. one of them is equal to zero) then it will display to the user "This problem cannot be solved".

xnew=xold-(fx/fxx)

I have tried to do this but it has not worked. not matching if and else!!

if ((fx=0)or(fxx=0));
{
xnew=xold-(fx/fxx);
}
else (cout<<"This problem cannot be solved.");


Some help would be great

aidan_walsh

= is assaignment.
== is equality comparison.

Overheal

Try some coding standard, too: its easier to read for example:

if ( a == 0 || b == 0 );
{
newX = oldX - ( a / b );
}
else { 
cout << "This problem cannot be solved." << endl;
}

You used the wrong brackets on the else statement. Also, for a one line else statement it is often acceptable (and compiler-acceptable) to not require brackets at all (as above)

But if you wanted to say else cout error message and return 0, you would need

else { // curly bracket required as the else covers more than one line of execution
cout << "cannot compute." << endl;
return 0;
}

so in your case you could write it like:

if ( a == 0 || b == 0 ) newX = oldX - ( a / b );
else cout << "This problem cannot be solved." << endl;

RosieJoe

chris85 wrote: »

Hi in a code i am writing i need to say that if numbers numbers (lets call them fx and fxx) are not equal to zero then it will perform the equation below.But if the if condition is not true (i.e. one of them is equal to zero) then it will display to the user "This problem cannot be solved".

xnew=xold-(fx/fxx)

I have tried to do this but it has not worked. not matching if and else!!

if ((fx=0)or(fxx=0));
{
xnew=xold-(fx/fxx);
}
else (cout<<"This problem cannot be solved.");


Some help would be great

Looking at this it looks like you have your logic backwards. From your free text it looks like you should be raising an error when either value is 0 not trying to evaluate the equation. If not, then you could have a divide by zero.

Try:

if ( a == 0 || b == 0)
{
cout << "This problem cannot be solved." << endl;
}
else
{
xnew = xold - (a/b);
}

chris85

RosieJoe wrote: »

Looking at this it looks like you have your logic backwards. From your free text it looks like you should be raising an error when either value is 0 not trying to evaluate the equation. If not, then you could have a divide by zero.

Try:

if ( a == 0 || b == 0)
{
cout << "This problem cannot be solved." << endl;
}
else
{
xnew = xold - (a/b);
}

Sorry meant this

if ((f<>0)and(fxx<>0))
{
xnew=xold-(fx/fxx)
}
else (cout<<"This problem cannot be solved.");


Anyway thanks for the help it is now working using the code given This is for engineering so dont know much about programming but the program is now working

Overheal

....................................................what.

nobody in their right mind would attempt using <> or >< as an operator and im not even sure its valid.

use != // not equal to

Naikon

Don't forget the && for the AND operator:)

chris85

Overheal wrote: »

....................................................what.

nobody in their right mind would attempt using <> or >< as an operator and im not even sure its valid.

use != // not equal to

Well the help menu says to use is as a not equal to operator but it doesnt work in the program so not valid.

Dont use this stuff much so sory if its stupid question

chris85

Also one more quick question guys. I output an answer to the user and it gives correct to say five decimal places. How can i get the program to give it to seven or eight decimal plaes. I think its something to do with adding in a line to set percision but aint working for me

Sherifu

chris85 wrote: »

Also one more quick question guys. I output an answer to the user and it gives correct to say five decimal places. How can i get the program to give it to seven or eight decimal plaes. I think its something to do with adding in a line to set percision but aint working for me

Something like << setprecision(8) << to specify decimal places afair.

Creamy Goodness

chris85 wrote: »

Also one more quick question guys. I output an answer to the user and it gives correct to say five decimal places. How can i get the program to give it to seven or eight decimal plaes. I think its something to do with adding in a line to set percision but aint working for me

what help menu, what IDE you using to write your C++?

double f =12.345678;
cout << setprecision (5) << f << endl; //prints 12.34568 rounds up only rounds up for the cout statement, the value in the variable is untouched.
cout << setprecision (9) << f << endl; //prints 12.345678 precision is bigger than actual double, precision is set set but the original double number is still the same.

DublinDilbert

Overheal wrote: »

....................................................what.

nobody in their right mind would attempt using <> or >< as an operator and im not even sure its valid.

use != // not equal to

Maybe he's thinking of VB where the not equal to operator is <>

chris85

Sorry yes writing it in VB.