Gets/fgets jumped over steps of input in C - c

Question

I have an exercise that I need to create a program to input all information of students as a student report as the source code below. I have a problem that I can't get a full stream input. It stepped over grade input and jumped to another student to input the next student's ID. I have put getchar() to get \n but it does not help. My problem is in the case 1 of the switch, so you just need to care only about it, the other cases do not make any sense in my question.
#include <stdio.h>
#include <string.h>
#define MAX 1000
typedef struct
{
char id[10];
char name[50];
float grade;
char assess;
}student;
char assess(int a)
{
if(a<4.00)
return 'F';
if(4.00<=a<6.00)
return 'D';
if(6.00<=a<7.00)
return 'C';
if(7.00<=a<8.50)
return 'B';
if(8.50<=a<10.00)
return 'A';
}
int main()
{
int choice;
int i=0, num=0;
int a=0, j=0;
student std[MAX], temp;
char search[50];
do
{
printf("Student Report\n");
printf("1.Input data\n2.Append data\n3.Sort data and print\n4.Search by names5.Quit\n");
printf("Your choice is: ");
scanf("%d", &choice);
switch(choice)
{
case 1:
{
do{
printf("How many students you want to add?\n");
scanf("%d", &num);
if(num<0 || num>50)
printf("Your number must be positive or smaller than or equal to 50!\n");
}while(num<0||num>50);
for(i=a; i<num; i++)
{
printf("Student's id No.%d:", i);
fgets(std[i].id, 10, stdin);
getchar();
printf("Student's name No.%d:", i);
fgets(std[i].name, 50, stdin);
getchar();
printf("Student's grade No.%d:", i);
scanf("%f", &std[i].grade);
std[i].assess=assess(std[i].grade);
}
a=num;
}
case 2:
{
do
{
printf("How many students you want to append?[0; %d]\n", MAX-num);
scanf("%d", &num);
}while(num<0||num>50-a);
for(i=a; i<num+a; i++)
{
printf("Student's id No.%d:", i);
fgets(std[i].id, MAX, stdin);
getchar();
printf("Student's name No.%d:", i);
fgets(std[i].name, MAX, stdin);
getchar();
printf("Student's grade No.%d:", i);
do
{
scanf("%f", &std[i].grade);
if(std[i].grade<0||std[i].grade>10)
printf("Please re-input grade, it must be between 0 and 10\n");
}while(std[i].grade<0||std[i].grade>10);
std[i].assess=assess(std[i].grade);
}
a=num+a;
}
case 3:
{
for(i=0; i<a; i++)
for(j=0; j<a; j++)
{
if(std[i].grade<std[j].grade)
{
temp=std[i];
std[i]=std[j];
std[j]=temp;
}
}
printf("ID\tName\t\t\tGrade\t\tAssessment\n");
for(i=0; i<a; i++)
printf("%-10s%-50s%-10.2f%-10c\n", std[i].id, std[i].name, std[i].grade, std[i].assess);
}
case 4:
{
printf("Student's name who you want to search: ");
fgets(search, MAX, stdin);
getchar();
for(i=0; i<a; i++)
if(strcasecmp(search, std[i].name)==0)
printf("%-10s%-50s%-10.2f%-10c\n", std[i].id, std[i].name, std[i].grade, std[i].assess);
}
case 5:
break;
default:
{
printf("Please reinsert your choice again\n");
break;
}
}
}while(choice!=5);
return 0;
}

Answer 1

The issue stems from \n not being consumed by scanf at first. To overcome the case I have added while ((c = getchar()) != '\n' && c != EOF);.
To get rid of \n character after fgets's usages, I'd prefer to use strcspn.
case 1:
{
do{
printf("How many students you want to add?\n");
scanf("%d", &num);
int c;
while ((c = getchar()) != '\n' && c != EOF);
if(num<0 || num>50)
printf("Your number must be positive or smaller than or equal to 50!\n");
}while(num<0||num>50);
for(i=a; i<num; i++)
{
printf("Student's id No.%d:", i);
fgets(std[i].id, 10, stdin);
std[i].id[strcspn(std[i].id, "\n")] = 0;
printf("Student's name No.%d:", i);
fgets(std[i].name, 50, stdin);
std[i].name[strcspn(std[i].name, "\n")] = 0;
printf("Student's grade No.%d:", i);
scanf("%f", &std[i].grade);
std[i].assess=assess(std[i].grade);
}
a=num;
break;
}
Moreover, asses function can be simplified as the following.
char assess(double a)
{
if(a < 4.00)
return 'F';
if(a < 6.00)
return 'D';
if(a < 7.00)
return 'C';
if(a < 8.50)
return 'B';
if(a < 10.00)
return 'A';
else
return -1; // the error indicator to be handled.
}
Further, after each case, you should put break statements. Glance at switch usage.

Answer 2

Based on the recommendation I found here - I am not able to flush stdin
We can use the below snippet to get rid of the junk in the buffer.
int c;
while ((c = getchar()) != '\n' && c != EOF);
Now the question is - where to put it in your program?
Well, I put it in the for loop and got the program to run and read all the three params - viz. ID, name, grade; for several entries of students.
Please check the below modified snippet from your program.
for(i=a; i<num; i++)
{
int c; // line 1 added
while ((c = getchar()) != '\n' && c != EOF); // line 2 added
printf("Student's id No.%d:", i);
fgets(std[i].id, 10, stdin);
printf("Student's name No.%d:", i);
fgets(std[i].name, 50, stdin);
printf("Student's grade No.%d:", i);
scanf("%f", &std[i].grade);
std[i].assess=assess(std[i].grade);
}