谁能给我解释一下%f和%d的用途吗?

#include <stdio.h>

 int main(int argc, const char * argv[])
 {

    float apples = 1.1;

    float bananas = 2.2;

    double fruit = apples + bananas;

    printf("%f.\n",fruit);

    return 0;

 }
#include <stdio.h>

 int main(int argc, const c