data.c

/********************
 * Exemplo por Luiz Felipe
 * https://github.com/Silva97
 ********************/

#include <stdio.h>
#include <unistd.h>

#define FNAME "exemplo.dat"

typedef struct data {
    char name[65];
    int  age;
} Data;

int main(){
    Data  user;
    FILE *dat;

    if(!access(FNAME, F_OK)){
        dat = fopen(FNAME, "r");

        fread(&user, sizeof user, 1, dat);

        printf("Seu nome:  %s\n", user.name);
        printf("Sua idade: %d\n", user.age);
    } else {
        fputs("Digite seu nome: ", stdout);
        scanf("%64[^\n]s", user.name);

        fputs("Digite sua idade: ", stdout);
        scanf("%d", &user.age);

        dat = fopen(FNAME, "w");

        fwrite(&user, sizeof user, 1, dat);
    }

    fclose(dat);
    return 0;
}