mirror of
https://github.com/hairrrrr/C-CrashCourse.git
synced 2026-03-24 05:51:14 +08:00
195 lines
3.0 KiB
C
195 lines
3.0 KiB
C
#include<stdio.h>
|
||
|
||
int main(void) {
|
||
|
||
printf("%+09d\n", 123);
|
||
printf("%-+09d\n", -123);
|
||
return 0;
|
||
}
|
||
|
||
int main(void) {
|
||
|
||
printf("%+09.2f\n", 12.3);
|
||
printf("%-8.3f\n", -12.3);
|
||
return 0;
|
||
}
|
||
|
||
int main(void) {
|
||
|
||
int len = 5;
|
||
int dec = 2;
|
||
printf("%*.*f\n",5, 2, 12.3);
|
||
printf("%*.*f\n",len, dec, 12.3);
|
||
return 0;
|
||
}
|
||
|
||
int main(void) {
|
||
|
||
printf("%hhd\n", (char)12345);//当作 1 个字节输出
|
||
printf("%hd\n", 12345);//当作 short 输出
|
||
return 0;
|
||
}
|
||
|
||
int main() {
|
||
|
||
int num;
|
||
printf("%d%n\n", 123, &num);
|
||
printf("%d\n", num);
|
||
|
||
return 0;
|
||
}
|
||
|
||
int main() {
|
||
|
||
int num;
|
||
scanf("%*d %d", &num);
|
||
printf("%d\n", num);
|
||
|
||
return 0;
|
||
}
|
||
|
||
int main(void) {
|
||
|
||
float x;
|
||
scanf("%g", &x);
|
||
printf("%F", x);
|
||
|
||
return 0;
|
||
}
|
||
|
||
int main(void) {
|
||
|
||
int num = 0;
|
||
int return_scanf = 0;
|
||
int return_printf = 0;
|
||
|
||
return_scanf = scanf("%d", &num);
|
||
return_printf = printf("%d\n", num);
|
||
|
||
printf("%d:%d\n", return_scanf, return_printf);
|
||
return 0;
|
||
}
|
||
|
||
|
||
FILE* fp = fopen("file", "r");
|
||
|
||
if (fp) {
|
||
fscanf(fp, ...);
|
||
fclose(fp);
|
||
}
|
||
else {
|
||
...
|
||
}
|
||
|
||
#include<stdio.h>
|
||
#include<stdlib.h>
|
||
#include "student.h"
|
||
|
||
void getList(Student* Stu, int num);
|
||
int save(Student* Stu, int num);
|
||
|
||
int main(void) {
|
||
|
||
int num = 0;
|
||
|
||
printf("请输入学生数量：\n");
|
||
scanf("%d", &num);
|
||
Student* Stu = (Student*)malloc(sizeof(Student) * num);
|
||
|
||
getList(Stu, num);
|
||
|
||
if (save(Stu, num)) {
|
||
printf("保存成功\n");
|
||
}
|
||
else
|
||
printf("保存失败\n");
|
||
|
||
return 0;
|
||
}
|
||
|
||
void getList(Student* Stu, int num) {
|
||
|
||
char format[STR_LEN];
|
||
sprintf(format, "%%%ds", STR_LEN - 1);
|
||
//向 format 中写入 %19s
|
||
//%%%ds 前两个%的意义是写入%
|
||
//%d 输出后面的参数，即：19
|
||
//最终写入的就是 %19s
|
||
|
||
int i = 0;
|
||
|
||
for (i = 0; i < num; i++) {
|
||
|
||
printf("第 %d 个学生 \n", i + 1);
|
||
printf("\t姓名：");
|
||
scanf(format, Stu[i].name);
|
||
printf("\t性别（0-男 1-女 2-其他）:");
|
||
scanf("%d", &Stu[i].gender);
|
||
printf("\t年龄:");
|
||
scanf("%d", &Stu[i].age);
|
||
//记得用scanf时，何时用 &
|
||
}
|
||
|
||
}
|
||
|
||
int save(Student* Stu, int num) {
|
||
|
||
int ret = -1;
|
||
FILE* fp = fopen("student.data", "w");
|
||
if (fp) {
|
||
ret = fwrite(Stu, sizeof(Student), num, fp);
|
||
//记录 fwrite 的返回值：写入文件的学生个数
|
||
fclose(fp);
|
||
}
|
||
else
|
||
printf("文件打开失败！");
|
||
|
||
return (ret == num);
|
||
//如果写入的个数不等于总人数，返回0
|
||
}
|
||
|
||
#include<stdio.h>
|
||
#include"student.h"
|
||
|
||
void read(FILE* fp, int index);
|
||
|
||
int main(void) {
|
||
|
||
FILE* fp = fopen("student.data", "r");
|
||
if (fp) {
|
||
fseek(fp, 0L, SEEK_END);//将文件读/写开始的位置定到结尾
|
||
long size = ftell(fp);//获得从文件开始到文件结尾的字节数
|
||
int index = 0;
|
||
int number = size / sizeof(Student);
|
||
printf("有 %d 个学生数据，你要看第几个\n", number);
|
||
scanf("%d", &index);
|
||
read(fp, index - 1);
|
||
}
|
||
else
|
||
printf("文件打开失败！\n");
|
||
}
|
||
|
||
void read(FILE* fp, int index) {
|
||
|
||
fseek(fp, index * sizeof(Student), SEEK_SET);
|
||
|
||
Student stu;
|
||
|
||
if (fread(&stu, sizeof(Student), 1, fp) == 1) {
|
||
printf("第 %d 个学生：\n", index + 1);
|
||
printf("\t姓名：%s\n", stu.name);
|
||
printf("\t性别：");
|
||
switch (stu.gender) {
|
||
case 0:
|
||
printf("男\n");
|
||
break;
|
||
case 1:
|
||
printf("女\n");
|
||
break;
|
||
default:
|
||
printf("其他\n");
|
||
break;
|
||
}
|
||
printf("\t年龄：%d\n", stu.age);
|
||
}
|
||
} |