22.改变文件中学生数据

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程序通过定义学生结构体变量，存储了学生学号、姓名和3门功课的成绩，所有学生数据均以二进制方式输出到student.dat中。函数fun的功能是从指定文件中找出指定学号的学生数据，读入此学生数据，对该学生的分数进行修改，使每门功课的分数加上3，修改后从写文件中该学生的数据，即用该学生的新数据覆盖原来的数据，其他学生数据不变，若找不到，则什么都不做。

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#define N 5typedef struct student{long son;char name[10];float score[3];}STU;void fun(char *filename, long sno){FILE *fp;STU n;int i;fp = fopen(filename, "rb+");while (!feof(fp)){fread(&n, sizeof(STU), 1, fp);if (n.son == sno)break;}if (!feof(fp)){for (i = 0;i < 3;i++)n.score[i] += 3;fseek(fp, -1L*(long)sizeof(STU), 1);fwrite(&n, sizeof(STU), 1, fp);}fclose(fp);}int main(){STU t[N] = { {10001,"NaoChao",91,92,77},{1002,"CaoKai",75,60,88},{10003,"LiSi",85,70,88},{10004,"FangFang",90,82,87},{10005,"ZhangSan",95,80,88} }, ss[N];int i, j;FILE *fp;fp = fopen("student.dat", "wb");fwrite(t, sizeof(STU), N, fp);fclose(fp);printf("\nThe original data:\n");fp = fopen("student.dat", "rb");fread(ss, sizeof(STU), N, fp);fclose(fp);for (j = 0;j < N;j++){printf("\nNo:%ld Name:%-8s Score:", ss[j].son, ss[j].name);for (i = 0;i < 3;i++)printf("%6.2f", ss[j].score[i]);printf("\n");}fun("student.dat", 10003);fp = fopen("student.dat", "rb");fread(ss, sizeof(STU), N, fp);fclose(fp);printf("The data after modifing:\n");for (j = 0;j < N;j++){printf("\nNo:%ld Name:%-8s Score:", ss[j].son, ss[j].name);for (i = 0;i < 3;i++)printf("%6.2f", ss[j].score[i]);printf("\n");}getchar();return 0;}

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