11 replies to this topic

[Detail]

Lesson 5

'IF' is a word which makes most of the world. It's also in C++.

If (expression)
ProgramStatement;

Note: There is no semicolon after the brackets.

The compiler evaluates the expression and if it's value is true ProgramStatment is executed, otherwise ProgramStatment is ignored.

If (expression)
ProgramStatement1;
Else
ProgramStatement2;

The compiler evaluates expression and if it's value is true ProgramStatement1 is executed, otherwise ProgramStatement2 is executed.

#pragma hdrstop
#include <iostream.h>
#include <conio.h>

int main()
{
  
  int Age;
  cout << "Please enter your age: ";
  cin >> Age;
  
  if(Age <= 21)
    cout << "You are young.";
  else
    cout << "You are old.";

  getch();

}

This code asks the user how old thay are, then insults them depending on there answer.

The code includes a "relational operator".
< is less than
> is greater/more than
>= is greater than or equal to
<= is less than or equal to
== is equal to
!= is not equal to

If the users answer is under 21 the program says "You are young", else is says "You are old".

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[Stino]

ProgramStarment and ProgramStatment, i think you mean ProgramStatement

[Phoib]

First real correction of Detail (Thanks to Olaf for confirming), in C++ its optional to use the curly braces.

If (expression)
ProgramStatement1;
Else
ProgramStatement2;

would become

If (expression) {
ProgramStatement1;
} Else{
ProgramStatement2;
}

[the_kid]

i was trying something like that the other day, and I had the ";" after teh ()... and it wouldn't work... it drove me crazy... But hopefully I will get it working now...

This is a funny program, give people the test to see if they are old...

[Stino]

Why do you have to use those {}?

[Detail]

You dont have to, there optional.
Thay help to orginise the code into sections.

[Mastermind]

To correct a correction, they are optional, but only for one line if statements. If you have more than one line in the if clause, you need to use the braces.
@ The_Kid: If you have that semicolon after the if, you create a condition that does nothing. It evaluates it, but finds no code, so your next line always gets executed, no matter what.

[Eradicator]

The { and } are equivalent to a begin and end in other languages. They signify where the code that is in something (if, case, function) starts and ends.

[the_kid]

I can't get it to work for words...

i have

#include <iostream>
#include <stdlib.h>

using namespace std;

int main(int argc, char *argv[])
{

  printf ("Testing stuff by: Michael Hedden\n\n\n\n");
  
 char rating;
  
  printf ("please tell me how well this works (good or bad): ");
  cin >> rating;
  
  if (rating==good)
  {
  
  cout << ("\n\nThank you for choosing Good.\n\n");
  }
  
  if (rating==bad)
  {
  printf ("\n\nReally... thats too bad\n\n");
  }
  
	system ("pause");
  return 0;
}

and it won't work...

[vice]

well, youre getting way over your head there pal. strings in C/C++ is a topic far too advanced for someone at your current level of ability.

however, i will just skim over the topic for you.

a string is basically an array of characters, or a bunch of letters put together. so in order to make a string you need to define an array of characters

char myString[256];
// this defines an array of characters, which can hold, at most, 256 letters

i'm sure arrays will be covered in upcoming lessons so i won't go into them at this moment.

getting strings from the user is also difficult for someone with your level of ability.
so for now just stick with the basic cout and cin with the basic (primitive) types i.e. int, double, boolean etc. don't worry about using printf just yet, you will just confuse yourself.

[Mastermind]

Otherwise, there is also getline, but that isn't easy to use either. Time will allow you to add more skills. Be patient, student.

[Banshee]

First real correction of Detail (Thanks to Olaf for confirming), in C++ its optional to use the curly braces.

If (expression)<!--QuoteEBegin-->ProgramStatement1;<!--QuoteEBegin-->Else<!--QuoteEBegin-->ProgramStatement2;

would become

If (expression) {<!--QuoteEBegin-->ProgramStatement1;<!--QuoteEBegin-->} Else{<!--QuoteEBegin-->ProgramStatement2;<!--QuoteEBegin-->}

You need braces if you will execute more than one command. I.e.:

Using braces:

#include<stdio.h>

void main (void)
{

int a,b,temp;

// grab numbers from user:
printf("Type 2 numbers: (i.e.: 1,2)");
scanf("%d,%d",&a,&b);

if (a < b)
{
   temp = b;
   b = a;
   a = temp;
}

// output:
printf("1st: %d and 2nd: %d",a,b);

}

if you insert "1,2", the output will be "1st: 2 and 2nd: 1".
if you insert "2,1", the output will be "1st: 2 and 2nd: 1".

Now, the same code without braces in the if:

#include<stdio.h>

void main (void)
{

int a,b,temp;

// grab numbers from user:
printf("Type 2 numbers: (i.e.: 1,2)");
scanf("%d,%d",&a,&b);

if (a < b)
   temp = b;

b = a;
a = temp;

// output:
printf("1st: %d and 2nd: %d",a,b);

}

if you insert "1,2", the output will be "1st: 2 and 2nd: 1".
if you insert "2,1", the output will be "1st: <trash> and 2nd: 2".

Trash will be a random number (trash), because temp wasnt initialized. The line temp = b; only runs when b > a, however the other 2 lines ignores the if...