Swapping the first and the last digit of any 5 random integers in C

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

void Swap(int n) {
    int a,length;
    char str[20];
    char temp1[1];
    char temp2[1];
    sprintf(str, "%d", n);
    length = strlen(str)-1;
    temp1[0] = str[0];
    temp2[0] = str[length];
    str[length] = temp1[0];
    str[0] = temp2[0];
    printf("\n%s\n",str);
}


int main()
{
    int i,lower,upper;
    lower = 90;
    upper = 9999;
    for (i = 0; i < 5; i++) {
        int rand_num = (rand() % (upper - lower + 1)) + lower;
        printf("\n%d\n ", rand_num);
        Swap(rand_num);

    }


}