making different number ranges execute unique tasks.

[sambo]

hi everybody. Im really new to programming and had a real quick question thats been baffling me. The program I am working on involves giving different responses depending on the number range it falls into from the information inputed. like 0 to 80 = this response and 80 to 100 = this and so on. '
my question is simply to see if im on the right track by using if statements.

code looks something like, "if (variable > 130) cout << certain sentence"

but i need to have 5 unique responses and the program doesnt work when i use 5 different if statements like

if (variable > 130) cout << certain sentence

else if (variable < 129 || variable > 100) cout << certain sentence

else if (variable < 99 || variable > 90) cout << certain sentence ect ect.

ive been looking online and still have not had any luck. should i try using a multidemensional array or something other than an if statement?

My gut tells me the if statement is the right track but im missing something crucial. any helpful hints would be mighty appreciated.

[helios]

This is the truth table for || (boolean OR):
A || B = C
A B C
F F F
F T T
T F T
T T T

This is the truth table for && (boolean AND):
A && B = C
A B C
F F F
F T F
T F F
T T T

Thus, A || B is true if A and/or B are true (that is, at least one has to be true), and A && B is true if both A and B and true.
Now, suppose we have the number x, and we want to evaluate x<15 || x>5. Let's take a look at what happens when x is 0, 10, and 20:
x = 0
x < 15 = T
x > 5 = F
T || F = T

x = 10
x < 15 = T
x > 5 = T
T || T = T

x = 20
x < 15 = F
x > 5 = T
F || T = T

As you can see, no matter what the value of x is, the expression always evaluates to true. That's because ALL numbers are >5 and/or <15.
Let's repeat the procedure, but now we'll evaluate x<15 && x>5
x = 0
x < 15 = T
x > 5 = F
T && F = F

x = 10
x < 15 = T
x > 5 = T
T && T = T

x = 20
x < 15 = F
x > 5 = T
F && T = F

This time, the expression only evaluated to true when x was in the range [6;14], but to false when x had any other value.

[h2owater]

else if (variable < 129 || variable > 100) cout << certain sentence

else if (variable < 99 || variable > 90) cout << certain sentence ect ect.

The above two cases are always true as || denotes 'OR' operation. Every integer should less than 129 OR greater than 100

It should be:

if (variable > 130) cout << certain sentence

else if (variable < 129 && variable > 100) cout << certain sentence

else if (variable < 99 && variable > 90) cout << certain sentence ect ect.

btw, the above code skipped the cases 100, 129,130, you may need to take care of these case as well

[Disch]

It should actually be neither of those.

You might notice that a value of 129 or 130 won't execute any of those paths. (130 is not > 130, and it's not < 129)

You don't need to have an upper and lower range for these. Just have a lower range. The 'else' takes care of the upper range automatically:

if(variable > 130)
  cout << "variable is > 130";
else if(variable > 100)
  cout << "no need for <= 130 because the 'else' ensures the value is <= 130.\n"
       << "all we have to do is say > 100";
else if(variable > 90)
  cout << "same thing";