Error in C program (for loops)

Question

void checker(int width,int height){
    int horizontal;
    int repeat;
    int i;
    int j;
    for(j=1; j<=height; j++){
        while(horizontal<=width){
            repeat = width/10;
            if(horizontal%2){
                for(i = 1; i <=repeat; i++)
                    printf("1");
            }
            else{
                for(i = 1; i <=repeat; i++)
                    printf("0");
            }
            horizontal++;
        }
        printf("\n");
    }
}

int main(){
    checker(20,10);

    return 0;
}

So I'm creating a pattern through C. As you can tell from my code, I'm barely getting the hang of C. As I compile and test this the pattern doesn't print out in 0's and 1's, rather it only prints the \n.

I was wondering why, I might be having a brain fart.

Thank you for the time, it's very appreciated from new comers like me!

You should post what you expected to see. Its hard for people to guess what you wanted from just non-working code! — kazagistar
– kazagistar, Commented Jan 29, 2016 at 21:03
Compile your code with all warnings & debug info (so gcc -Wall -Wextra -g if using GCC...). Learn to use the debugger (gdb) — Basile Starynkevitch
– Basile Starynkevitch, Commented Jan 29, 2016 at 21:08

camel-man · Accepted Answer · 2016-01-29 20:59:14Z

3

Horizontal is not properly initialized. Right now you are using garbage value left in memory. Give horizontal a proper value before trying to use it.

answered Jan 29, 2016 at 20:59

camel-man

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Comments

jackmott · Accepted Answer · 2016-01-29 21:50:58Z

2

horizontal has not been initialized. unlike some languages, C will not default a non static local variable to 0. It will be just whatever value happens to be in memory.

edited Jan 29, 2016 at 21:50

answered Jan 29, 2016 at 20:59

jackmott

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1 Comment

Michi Over a year ago

C will not default a value to 0 Are you sure about that ? How about for example global and static variables which are stored in Data Segment?

ryyker · Accepted Answer · 2016-01-29 21:51:46Z

1

Change/add line(s):

int horizontal;//not guaranteed to be zero

to

int horizontal = 0;//guaranteed to be zero

Otherwise, this statement may never enter the brackets

while(horizontal<=width){ ...

Also (not required, but maybe nice to have) add this line just after int j;...

...
int j;

if((width < 0) || (height < 0)) return; //prevent negative input values

answered Jan 29, 2016 at 21:51

ryyker

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