Why isn't my do while statement working [closed] - c++

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Closed 9 years ago.
Can you please fix this program. It will not cout z.
int main()
{
using namespace std;
int x, y, z, a;
cout << "Please enter a number" << endl;
cin >> x;
cout << "Please enter another number" << endl;
cin >> y;
cout << "What do you want to do with these numbers?" << endl;
cout << "1 = +" << endl;
cout << "2 = -" << endl;
cout << "3 = *" << endl;
cout << "4 = /" << endl;
cin >> a;
do {
z = add(x, y);
} while (a == 1);
do {
z = sub(x, y);
} while (a == 2);
do {
z = mul(x, y);
} while (a == 3);
do {
z = dis(x, y);
} while (a == 4);
cout << z;
return 0;
}
I tried using the do while statement, but I can not get it to work.
---EDIT---
Added proper indenting, why wont it do so atomatically?

Answer 1

Whichever option you enter, its going to enter that do-while loop and never exit because the condition will always be satisfied. Ex. if i enter 1 then it will enter :
do {
z = add(x, y);
} while (a == 1);
and since a will always be 1 it will never exit this. Same is the case with the other conditions. Instead you could use a switch statement. Something like :
switch(a) {
case 1 : z = add(x, y);
break;
case 2 : z = sub(x, y);
break;
case 3 : z = mul(x, y);
break;
case 4 : z = div(x, y);
break;
default : cout<<"Please choose a valid option to proceed.";
}
cout << z;
return 0;
Also, you do not use do-while in such cases. Even if you exit the loop, it will always divide(x, y) since do-while is such that it enters and then sub-sequently checks for the condition. You could however use a while loop something like this :
while(a==1) {
z = add(x, y);
a = -1;
}
while(a==2) {
z = sub(x, y);
a = -1;
}
while(a==3) {
z = mul(x, y);
a = -1;
}
while(a==4) {
z = div(x, y);
a = -1;
}

Answer 2

The statement:
while( 1 >= a <= 4)
is incorrect [well, it's correct C syntax, but it's most likely not what you wanted, since it does]:
while( (1 >= a) <= 4);
And since the result of (1 >= a) is either 0 or 1, it is always <= 4. You need to do:
while ( (1 >= a) && (a <= 4) );
[Parenthesis simply for clarity, you can remove the two inner sets of parenthesis]

Answer 3

Your code is entering an infinite loop, modify it like so
int main()
{
using namespace std;
int x, y, z, a;
do
{
cout << "Please enter a number" << endl;
cin >> x;
cout << "Please enter another number" << endl;
cin >> y;
cout << "What do you want to do with these numbers?" << endl;
cout << "1 = +" << endl;
cout << "2 = -" << endl;
cout << "3 = *" << endl;
cout << "4 = /" << endl;
cin >> a;
switch(a)
{
case 1:
z = add(x, y);
break;
case 2:
z = sub(x, y);
break;
case 3:
z = mul(x, y);
break;
case 4:
z = dis(x, y);
break;
}
cout << z;
} while( 1 >= a <= 4)
return 0;
}
modified as per lokoko's suggestion