 Banfa  9,065
Recognized Expert Moderator Expert
I felt that this was a good point to start a tutorial on C/C++ programming because clearly we need to have some idea of what we are trying to achieve before we start out. I recently found this definition on the web which I rather like "Programmin g is planning how to solve a problem. No matter what method is used -- pencil and paper, slide rule, adding machine, or computer -problem solving requires programming. Of course, how one programs depends on the device one uses in problem solving."
This is taken from the ROYAL PRECISION, Electronic Computer PROGRAMMING MANUAL for the LGP-30. For those of you that have not heard of the LPG-30 you may be forgiven because it was first made in 1956 and has long since gone out of production. But it has the rather auspicious claim of being the type of computer that Edward Lorenz was using when he first noted the chaotic nature of weather systems.
Anyway back to what is programming... "planning how to solve a problem", note we are not actually solving a problem, the computer is going to do that for us. If we could solve the problem ourselves we would have no need to write the program. The premise for a program is that we don't have the time, tenacity or memory capabilities to solve a problem but we do know how to solve it so can instruct a computer to do it for us.
A simple example of this is what is the sum of all integers from 1 - 10,000. If you wanted to you could sit down with a pencil and paper or a calculator and work this out however the time involved plus the likelihood that at some point you would make a mistake makes that an undesirable option. However I can write and run a program to calculate this sum in less than 5 minutes -
#include "stdio.h"
-
-
#define MAX (10000UL)
-
-
int main(int argc, char **argp)
-
{
-
unsigned long sum = 0;
-
unsigned long number;
-
-
for(number=1; number<=MAX; number++)
-
{
-
sum += number;
-
}
-
-
printf("The sum of all integers from 1 - %lu is: %lu\n", MAX, sum);
-
-
return 0;
-
}
-
This gives the result 50005000. As it happens I can verify this because I know that the sum of integers from 1 - N can be calculated as
(N+1)*(N/2)
(10000 + 1)*(10000/2) = 10001*5000 = 50005000
So I have solved the problem of how to calculate the sum of all integers from 1 - 10000 and the computer has solve the problem of calculating the sum of all integers from 1 - 10000.
And this is the crux of all computer programs; you can not program a computer to solve a problem unless you know how to solve that problem. There is no point even sitting at your computer with the intention of programming until you have the knowledge, be that a formula from a text book or a design document or a print out from a web page, of how you are going to set about solving the problem.
So programming is the production of a set of instructions that describe how a problem can be solved. There are many languages in which these instructions may be written, for instance on the back of a bottle of shampoo you will often find the instructions describing how to solve the problem of making dirty hair clean: - Wet hair
- Rub in shampoo to create a lather
- Rinse Hair
- Repeat
Note that because this set of instructions is aimed at human beings it makes a couple of assumptions. In step 4 for instance it makes the assumption that normal English is in use and that the instruction will actually be read as “Repeat Once”. It is also likely that an human running these instructions will not repeat step 1 because their hair will already be wet so they will judge it unnecessary to repeat that step.
And that is one of the major differences between humans and computers. Humans have judgement and free will and will not run any instruction they deem not required or nonsensical where as a computer will do exactly what it is told with no judgement on the need or sanity of the instruction. Give the instructions above to your computer and it will never get out of the shower. Tutorial 2: How to Program 17 79400 
Thats a pretty cool write-up; very clearly put.
Arguably programming is expressing the plan in a way that the computer can accept; not merely making the plan, however what you wrote is so good and clear, I won't actually argue the point.
Nice!
Sam
sorry, but your example is very sloppy code.
* you return 0, why not RETURN_SUCCESS?
* why don't you check the return code of printf()?
* if your unsigned long types were 16 bit, your total would overflow
* printf("%lu", MAX) is not correct. your #define is replaced by a signed integer
* printf("%lu", MAX) is not correct if your unsigned long type is larger than an integer (eg. 32-bit int, 64-bit long)
* most compilers will take #include "stdio.h" to mean looking local directory first, then system/compiler flag listed directories. your should use #include<stdio. h>
And we have almost developed a plan for solving the problem of how to do programming just like nature did right?
personally i prefer to write my code like this... -
x=0
-
(1..10000).each{ |i| x+=i }
-
puts "The sum of all integers from 1 - 10000 is: #{x}"
-
name that language!
Looks like a type of old Basic, i remember puts, was in Apple, TI, Commodore or TRS-80, not sure which one, been awhile :P
Banfa 9,065
Recognized Expert Moderator Expert
* you return 0, why not RETURN_SUCCESS?
Returning 0 is defined as an acceptable indication of success by the C standard, it is guaranteed to work for a conforming compiler and I see no reason not to use it. Also I think you mean EXIT_SUCCESS.
* why don't you check the return code of printf()?
And do what if it has failed? I suppose return EXIT_FAILURE but for the purposes of this small example program that seems like over engineering to me for a function that in such a simple program really should be expected to work on any platform with a stdout.
* if your unsigned long types were 16 bit, your total would overflow
As it would if the unsigned long where 7 bit, 13 bit or any other uncommon number. However in my years of experience of programming 8, 16, 32 and 64 bit machines I have yet to see a platform where unsigned long was not 32 bits (although it arguably should be on todays 64 bit PCs). I am not saying it is not possible or that such machines do not exist but I get the impression they are quite rare and I suspect anyone trying this code on such a machine is likely to be aware this.
* printf("%lu", MAX) is not correct. your #define is replaced by a signed integer
* printf("%lu", MAX) is not correct if your unsigned long type is larger than an integer (eg. 32-bit int, 64-bit long)
I concede both points, I have changed my #define to define the constant as a unsigned long constant to make all the types match.
* most compilers will take #include "stdio.h" to mean looking local directory first, then system/compiler flag listed directories. your should use #include<stdio. h>
A bit of a nit pick but I have change the code to fix this.
Banfa 9,065
Recognized Expert Moderator Expert
name that language!
Nope I can't and Google is letting me down badly, I have to admit to having my curiosity piqued and would like to know the answer.
Banfa 9,065
Recognized Expert Moderator Expert
Arguably programming is expressing the plan in a way that the computer can accept; not merely making the plan, however what you wrote is so good and clear, I won't actually argue the point.
Nice!
Sam
Thanks Sam :D
personally i prefer to write my code like this...
-
x=0
-
(1..10000).each{ |i| x+=i }
-
puts "The sum of all integers from 1 - 10000 is: #{x}"
-
name that language!
I may be wrong, but this looks like ruby to me.
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