#include <stdio.h>
#include <ctype.h>

void put_in_spaces(char word[]);

int main() {

    char string[] = "How_are_you, Mr. Burns? R2D2 will n0w see you @ noon.";
    put_in_spaces(string);
    printf("%s\n",string);
    return 0;
}

void put_in_spaces(char word[]) {

    int i = 0;
    while (word[i] != '\0') {

        if (!isalpha(word[i]))
            word[i] = ' ';
        i++;
    }
}