Concatenate first characters from a command line argument in c

Question

I have tried this solution, but don't know why it is giving segmentation fault.

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[])
{
    char st[1000]="";
    for (int i=1; i<argc; i++)
    {

            strcat(st,argv[i][0]);
            strcat(st,". ");

    }
    printf("%s", st);

    return 0;
}

Answer 1

Change this statement

        strcat(st,argv[i][0]);

to

        strncat(st, &argv[i][0], 1);

or

        strncat(st, argv[i], 1);

In the original statement the function considers the character argv[i][0] as a pointer value. So the call has undefined behavior.

Or you can use a straightforward approach without using string functions. For example

#include <stdio.h>

int main( int argc, char * argv[] ) 
{
    char st[1000];
    size_t i = 0;

    for ( int j = 1; j < argc; j++ )
    {
        st[i++] = *argv[j];
        if ( j + 1 != argc )
        {
            st[i++] = ',';
            st[i++] = ' ';
        }           
    }

    st[i] = '\0';

    puts( st );

    return 0;
}