C++ Tutorial/Operators statements/if statement

A block of code in if statement

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 double result, n, d; 

 cout << "Enter value: "; 
 cin >> n; 

 cout << "Enter divisor: "; 
 cin >> d; 

 if(d != 0) { 
   cout << "d does not equal zero so division is OK" << "\n"; 
   result = n / d; 
   cout << n << " / " << d << " is " << result; 
 } 

 return 0; 

}</source>

Enter value: 12
Enter divisor: 21
d does not equal zero so division is OK
12 / 21 is 0.571429"

A nested if tatement

<source lang="cpp">#include <iostream>

int main()
{
    int firstNumber =2;
    int secondNumber = 3;

    if (firstNumber >= secondNumber)
    {
        if ( (firstNumber  secondNumber) == 0) // evenly divisible?
        {
            if (firstNumber == secondNumber)
                std::cout << "They are the same!\n";
            else
                std::cout << "They are evenly divisible!\n";
        }
        else
            std::cout << "They are not evenly divisible!\n";
    }
    else
        std::cout << "Hey! The second one is larger!\n";
    return 0;
}</source>

Hey! The second one is larger!

An if-else-if ladder.

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 int x; 

 for(x=0; x<6; x++) { 
   if(x==1) cout << "x is one\n"; 
   else if(x==2) cout << "x is two\n"; 
   else if(x==3) cout << "x is three\n"; 
   else if(x==4) cout << "x is four\n"; 
   else cout << "x is not between 1 and 4\n"; 
 } 

 return 0; 

}</source>

x is not between 1 and 4
x is one
x is two
x is three
x is four
x is not between 1 and 4

If else statement with block code

<source lang="cpp">#include <iostream>

1. include <cstdlib>

using namespace std;

int main() {

 int magic;  // magic number 
 int guess;  // user"s guess  

 magic = rand(); // get a random number 
  
 cout << "Enter your guess: "; 
 cin >> guess; 

 if (guess == magic) { 
   cout << "Right\n"; 
   cout << magic << " is the magic number.\n"; 
 } 
 else { 
   cout << "...Sorry, you"re wrong."; 
   if(guess > magic) 
      cout <<" Your guess is too high.\n"; 
   else 
      cout << " Your guess is too low.\n"; 
 } 

 return 0; 

}</source>

Enter your guess: 3
...Sorry, you"re wrong. Your guess is too low.

If statement with else

<source lang="cpp">#include <iostream>

1. include <cstdlib>

using namespace std;

int main() {

 int magic;  // magic number 
 int guess;  // user"s guess 

 magic = rand(); // get a random number 
  
 cout << "Enter your guess: "; 
 cin >> guess; 

 if(guess == magic) 
     cout << "Right"; 
 else 
     cout << "...Sorry, you"re wrong."; 

 return 0; 

}</source>

Enter your guess: 3
...Sorry, you"re wrong."

if statement with variable logic operators

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 int a, b, c;  
 
 a = 2;  
 b = 3;  
 
 if(a < b) 
    cout << "a is less than b\n"; 

 if(a == b) 
    cout << "you won"t see this\n";  

 cout << "\n"; 

 c = a - b;

 cout << "c contains -1\n"; 
 if(c >= 0) 
    cout << "c is non-negative\n"; 
 if(c < 0) 
    cout << "c is negative\n"; 

 cout << "\n"; 

 c = b - a; // c now contains 1 
 cout << "c contains 1\n"; 
 if(c >= 0) 
    cout << "c is non-negative\n"; 
 if(c < 0) 
    cout << "c is negative\n"; 

 return 0; 

}</source>

a is less than b
c contains -1
c is negative
c contains 1
c is non-negative

if with else

<source lang="cpp">#include <iostream>

int main()
{
    int firstNumber, secondNumber;
    std::cout << "Please enter a big number: ";
    std::cin >> firstNumber;
    std::cout << "\nPlease enter a smaller number: ";
    std::cin >> secondNumber;
    if (firstNumber > secondNumber)
        std::cout << "\nThanks!\n";
    else
        std::cout << "\nOops. The second is bigger!";
    return 0;
}</source>

Please enter a big number: 123
Please enter a smaller number: 12
Thanks!

Proper use of braces with an if statement

<source lang="cpp">#include <iostream>

int main()
{
    int x = 12;
 
    if (x > 10)
    {
        if (x > 100)
            std::cout << "More than 100, Thanks!\n";
    }
    else        // now works as intended!
        std::cout << "Less than 10, Thanks!\n";
    return 0;
}</source>

Use an int value to control the if

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 int a, b; 

 cout << "Enter numerator: "; 
 cin >> a; 
 cout << "Enter denominator: "; 
 cin >> b; 

 if(b) 
    cout << "Result: " << a / b << "\n"; 
 else 
    cout << "Cannot divide by zero.\n"; 

 return 0; 

}</source>

Enter numerator: 2
Enter denominator: 4
Result: 0