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

int main(int argc, char** argv) {
    char input_string[] = "Hello!";

    int size = strlen(input_string);

    char output_string[size+1]; // Make space for a new string of the same size (remember the zero termination)

    for (int i = 0; i < size; i++) {
        // Take the first char of input_string and put at the last entry etc.
        // Think of the edge cases. When i = 0, we should take input_string[0]
        // and put in output_string[size-1].
        output_string[size - i - 1] = input_string[i];
    }

    printf("%s\n", output_string);

    return 0;
}