[SOLVED] Simple C program, can't understand the output.

moisespedro · 11-11-2014, 03:51 PM

Hi, I am reading a C book and it asked the reader to print the following output:

Code:

1
12
123
.
.
.
12345678910

Since it is an example, the book has the code ready:

Code:

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

        for(i=1;i<=10;i++) {
                for(j=1;j<=i;j++)
                        printf("%d",j);
                putchar('\n');
        }
}

It works, yes indeed but I didn't understand how. I mean, in my head it would print j once, sum 1 to j, check if it is less than i and then print it again.

In my head the output would be:

Code:

What am I missing?

suicidaleggroll · 11-11-2014, 03:56 PM

Why do you think it would just print j once? j is inside a loop from 1 to i.

So when i is 1, j will loop from 1 to 1, and print 1
Then it will print a new line
Then when i is 2, j will loop from 1 to 2, and print 12
Then it will print a new line
And so on through 10.

Maybe what you're missing is the fact that in C, when you have a for loop or if statement, if there are no {}, it will include everything up to the next ; as part of the block.

So:

Code:

for(j=1;j<=i;j++)
   printf("%d",j);

Code:

for(j=1;j<=i;j++) printf("%d",j);

Code:

for(j=1;j<=i;j++) {
   printf("%d",j);
}

are all equivalent.

moisespedro · 11-11-2014, 04:02 PM

Oh, thanks. Now I've got it.