Issue with for loop in C, scanf() in initialization

Question

I've tried to refractor my very very easy programm (I'm beginner, sorry for stupidity). I wanted to put scanf() into first paragraph of loop initialization and I thought that everything would have been alright but it doesn't work as I had "predicted". The programm should get and intiger and then write following numbers till the last number would be 10 times bigger tahn the first one but instead of this it writes out numbers from 1 to the number 10 times bigger. I would be grateful for any tips and debugg. Have a nice day!

Code:

 #include <stdio.h>
int main()
{
  int x, i;

  printf("Please put intiger:\n");

  for(i = (scanf("%d", &x)); i < x + 10; i++)
    printf("%d\n", i);

  return 0;


}

Execution:

Please put intiger: 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Press any key to continue . . .

P.P · Accepted Answer · 2020-04-12 11:46:37Z

1

scanf returns the number of values it has successfully scanned, not the value of input you have given. But what you wanted is to to print 10 numbers starting x.

You'd need:

scanf("%d", &x);
for (i = x; i < x + 10; i++) 
    printf("%d\n", i);

Read the documentation of scanf for what it returns. Also remember scanf could fail too.

answered Apr 12, 2020 at 11:46

P.P

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3 Comments

Peter - Reinstate Monica Over a year ago

Re "Also remember scanf could fail too": Which is why you always check the return value and balk if it is not what you expect.

stalker.exe Over a year ago

Thank you very much, firstly i had done it like u have shown but i thought i can make it easier, now i will remember i cannot:(

P.P Over a year ago

By "easier" you mean, combine the input in the loop itself, you can do with comma operator: for (i = (scanf("%d", &x), x); i < x + 10; i++) But I wouldn't call this easier or recommend. This also doesn't allow error checking of scanf.

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