How to use scanf in C.

[twitch]

A lot of new C programmers have trouble with scanf(). So I'm going to show you how to do it

The main reason beginners have trouble is scanf works like a pointer so you have to point to what your getting input for

#include<stdio.h>

int main()
{
   int myvariable;

   printf("Enter a number:");
   scanf("%d",&myvariable);
   printf("%d",myvariable);
   
   return 0;
}

See when we used scanf we first declared what the variables type was
"%d" for int ,"%f" for float ,%e for double ,"%c" for char , "%s" for strings.

Then in the second part we have to use & like in a pointer to point to the variable instead of just getting its value Remember without & your program will likely crash

For handling strings with space and in files use fgets Here is a link to a tutorial on using it User Input: Strings and Numbers [C]

[v0id]

Actually a nice little tutorial, I like your coding style, it's clean and the layout of the tutorial is too. Good job.

[John]

Nice tutorial, but even though I know how to use scanf now, I have no idea what it is used for

When/Why is scanf() used?

[v0id]

Originally Posted by Sidewinder

Nice tutorial, but even though I know how to use scanf now, I have no idea what it is used for

When/Why is scanf() used?

You're using scanf() to get userinput in C, like you're using std::cin in C++.

[rong889]

Nice tutorial.

[G_Morgan]

I'll comment on scanf since I think it's an awful function. Scanf expects data of the correct type. If you enter in the wrong data then it fails to work. Now you can catch this by catching the return code, scanf returns the number of items it read in so if it returns 0 you know that it failed on the first entry. You may think this appropriate

int check = 1;
int var = 0;
while(check){
    check = !scanf("%d", &var);
}

Since there's only one variable read, it will either return 0 on failure or 1 on success. The ! inverts this and check feeds it back into the while loop (so that this will loop until there is correct input).

You may think job done. Unfortunately scanf doesn't flush the input buffer on failure so if I enter 'error' it will stay on the input buffer for the next time, this program gives an infinite loop on an error.

So what can we do? We could call fflush(stdin); but this behaviour is undefined according to the C standard. Windows happens to define fflush on stdin but I've seen code elsewhere which doesn't work.

Personally I prefer to use fgets.

char buff[20];
fgets(buff, size, stdin);

and then parse the output. It certainly doesn't leave mess on stdin and is fully portable. Once you've got a set of functions written to do this you won't ever need to touch temperamental scanf again. The one thing to be careful of, fgets leaves the newline character on the end of the output so you will want to write a function that scans it and replaces it with the null character.

[catherine sea]

it is a perfect tutorial for rookies