Error Segmentation fault (core dumped)

Question

I am doing some exercises for my university course on C and I have the following code which exits with error Segmentation fault (core dumped) after the user has input the choice (1 or 2). I don't know if it's an issue that I am using ubuntu 16.04 and I am compiling my source code files with make command. Oh and please don't recommend to use the built-in c function strcpy because this exercise is supposed to "teach us' how to make our own string copy.

So what am I doing wrong?

#include <stdio.h>
#define SIZE 1000

char mystrcpy(char *dest,char *src);

main(){

    char str1[SIZE];
    char str2[SIZE];
    char str3[SIZE];
    int choice;



    printf("Give first string: ");
    gets(str1);
    printf("Give second string: ");
    gets(str2);
    printf("Choose one of two strings (1 h 2): ");
    scanf("%d",&choice);

    if (choice==1)
        mystrcpy(str3,str1);
    else (choice==2)
        mystrcpy(str3,str2);

    printf("\nFirst string is %s\n",str1);
    printf("\Second string is %s\n",str2);
    printf("\nThrid string is %s\n",str3);

}


char mystrcpy(char *dest,char *src){
    int i;

    while(1)
    {

        dest[i] = src[i];
        if (src[i] == '\0')
            break;

        i++;
    }

    return dest;
}

Answer 1

i is never initialized. (need 30 characters....)

Answer 2

You are not initializing i , so it starts at an indeterminate value, hence the segfault.

Notice that enabling the warnings would have shown this problem immediately in this simple case; in more complicated scenarios using a debugger would have shown that the value of i at the moment of crash would have been completely nonsensical.