C ++条件语句

Question

Note: Leaning C++ background with python background

Looking at the last if statement of the code below: what does i=1 mean after the if statement. Looking at the last else statement. what does the i=0 mean after the else statement? Why are they there

#include <stdio.h> // preprocessor command
int foo(int x) // function definition
{ 
return x+1; // return expression value
}

int main() // this is where all C programs start
{
    int i = 0; // variable definition + init.
    while (i < 10) 
    { // loop + condition
        i = i+1; // expression + assignment
        printf("%d ", foo(i)); // function calls, output
    }
    if (i >= 10) i = 1; // conditional code execution
    else i = 0;
    return i; // return result, exit function
}

Answer 1

In your example, i=1 is a assignment sentence not included in if -statement, not a conditional code. It's equivalent to

if (i >= 10) // conditional code
    i = 1; // will execute if i>=10

or more clearer

if (i >= 10) // conditional code
{
    i = 1; // will execute if i>=10
}

If you want, not recommended though, you can write all the code in one line.

You should be aware of the indent style of different languages:

Indentation is not a requirement of most programming languages, where it is used as secondary notation. Rather, programmers indent to better convey the structure of their programs to human readers. In particular, indentation is used to show the relationship between control flow constructs such as conditions or loops and code contained within and outside them. However, some programming languages (such as Python and Occam) use the indentation to determine the structure instead of using braces or keywords.

Answer 2

It's just a one-line if statement. When there is only one line to be executed you don't need the braces.

Answer 3

Try changing your code to::

 #include <stdio.h> // preprocessor command
 int foo(int x) // function definition
  { 
  return x+1; // return expression value
  }

  int main() // this is where all C programs start
       {
        int i = 0; // variable definition + init.
while (i < 10) 
{ // loop + condition
    i = i+1; // expression + assignment
    printf("%d ", foo(i)); // function calls, output
}
if (i >= 10) {
         i = 1; // conditional code execution
      }else{
     i = 0;
   }
  return i; // return result, exit function
 }

you should be very careful with the braces while using loop, after if condition as in if(i<10) if you put braces then only your control will move inside the loop based onb the conditions mentioned in the loop.

Answer 4

They are the C/C++ equivalent to Python 3's

i = 1 if i >= 10 else 0

In C++ the if / else keywords take a statement:

if ( condition )
    <statement>
[else if ( condition ) 
    <statement>]
[else
    <statement>]

A statement is a clause, terminated by a semicolon, eg a = b;, or a compound statement, enclosed in {}s, eg

if ( a == 1 )
    std::cout << "a is one\n";
if ( a == 2 ) {
    std::cout << "a is two\n";
    return 0;
}

C++ largely does not care about whitespace. So the above is equivalent to

if(a==1)std::cout<<"a is one\n";if(a==2){std::cout<<"a is two\n";return 0;}

or

if ( a
== 1 )
{
    std :: cout
    <<
    "a is "
    "one"
    "\n";
}  if  // horrible but legal.
(
    a ==
          2)
{ std ::
   cout
     <<
       "a is two"
         "\n"
           ;
             return
               0
                 ;
               }

or various other permutations :)

Answer 5

C/C++ does require to separate code blocks by using indentations, in contrast to python.

If the statement after an if/else is a single item, it does not require braces.

if(x) a(); else b();

is equivalent to:

if(x){ a(); }else{b();}

and:

if(x)
{
    a();
}
else
{
    b();
}

Answer 6

They are the C/C++ equivalent to Python

i = [1 if i >= 10 else 0]

In C++ the if / else keywords take a statement:

if ( condition )
    <statement>
[else if ( condition ) 
    <statement>]
[else
    <statement>]

A statement is a clause, terminated by a semicolon , eg a = b; , or a compound statement, enclosed in {}s, comprising one or more semicolon-terminated statements or compound statements

statement :=
    statement-text ';' |
    '{' statement '}'

As follows:

if ( a == 1 )
    std::cout << "a is one\n";
if ( a == 2 ) {
    std::cout << "a is two\n";
    return 0;
}

C++ largely does not care about whitespace. So the above is equivalent to

if(a==1)std::cout<<"a is one\n";if(a==2){std::cout<<"a is two\n";return 0;}