simple question on string concat

Applications Programming
1

This is a simple question...

char *str = NULL;
int  num = 0;
scanf ("%d", &num);
str = ???

I want str to point to the string num.txt

For e.g: If user enters num = 5,

str should point to "5.txt"

How do I do that ?

Thanks

2

char buf[10];

snprintf(buf,sizeof(buf),"%d.txt",num);

str=buf;

3 
/* try */
snprintf(buf,sizeof(buf),"%d.txt",num);