concatenate each value of argv with a string - c

Question

I'm working on a C program that get the command line arguments and append to them a file extension.
The execution will be something like this:
>myprogram file1 file2
and will execute another program that will use as argument file1.txt and file2.txt.
I tried doing that would add the extension and run one command (s1 is the path and s2 is argv[i] on a loop:
int getfile(char *s1, char *s2){
char *str2 = malloc(sizeof(s2)+3);
strcpy(str2,s2);
strcat(str2,".txt");
execl(s1,"program",str2,NULL);
exit(0);
}
The function will run the program for one file (>program file1.txt and >program file2.txt), but I will need to find a way to run it this way (>program file1.txt file2.txt).
I tried to modify argv directly, but I was unsuccessful.
Any advise?

Answer 1

Try this code:
int main(int argc, char *argv[])
{
char *buffer;
char command[512];
int i = 1;
for(i = 1; i < argc; i++){
buffer = malloc(strlen(argv[i]) + 5);
strcpy(buffer,argv[i]);
strcat(buffer,".txt");
sprintf(command,"touch %s\0",buffer);
system(command);
free(buffer);
}
return 0;
}
A simple program that has no error checking, and I like to explicitly add the string terminator.

Answer 2

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, int *argv[]){
if(argc==1){
printf("You have not entered anything!\n");
return 0;
}
char *arr=malloc(1000*sizeof(char));
int i;
strcat(arr, argv[0]);
strcat(arr, " ");
for(i=0;i<argc-1;i++){
strcat(arr,argv[i+1]);
strcat(arr,".txt");
strcat(arr," ");
strcat(arr,"\0");
}
printf("%s\n",arr);
free(arr);
return 0;
}