using fgets with structure - c

Question

I am trying to use fgets with structure, since I have to insert in character array. But when I use fgets it's not working properly. I can not enter value for the char array. Please help. Below is a sample program::
#include <stdio.h>
#include<string.h>
struct Student
{
int roll;
char name[50];
int age;
char branch[50];
char gender[1]; //F for female and M for male
};
int main()
{
struct Student s1;
printf("enter roll number of the student: ");
scanf("%d", &s1.roll);
printf("Enter student name: ");
fgets(s1.name, 50, stdin); // NOT WORKING ...
printf("Enter age number: ");
scanf("%d", &s1.age);
printf("Enter branch number: ");
scanf("%d", &s1.branch);
printf("Enter Gender: ");
scanf("%d", &s1.gender);
return 0;
}

Answer 1

First of all you need different format specifiers for different datatypes. So you need to use %c for a character and %[^\n] for a string containing spaces.
You also need to remove leading whitespaces before scanning a string, because a newline \n is left in the input buffer which would otherwise be read by %c and %[], as Weather Vane pointed out in a comment.
#include <stdio.h>
#include <string.h>
struct student
{
int roll;
char name[50];
int age;
char branch[50];
char gender; // can be a single character
};
int main(void)
{
struct student s1;
printf("Enter roll number: ");
scanf("%d", &s1.roll);
printf("Enter name: ");
scanf(" %49[^\n]", s1.name); // use %[^\n] to scan a string containing spaces
printf("Enter age: ");
scanf("%d", &s1.age);
printf("Enter branch name: ");
scanf(" %49[^\n]", s1.branch);
printf("Enter gender: ");
scanf(" %c", &s1.gender); // %c is the format specifier for a char
return 0;
}

Answer 2

fgets is not being bypassed, it's actually working as it should, what happens is that it reads the newline character that remains in the input buffer from the previous scanf, if you access s1.name you will see that it has a string ("\n\0") in it.
For name I have to insert space character too, so I used fgets
You can use scanf with [^\n] specifier which can read spaces. Mixing scanf with fgets is trouble, it can be done, but you should avoid it.
You should either use scanf only, or fgets only, in the latter case, if you need to convert strings to ints use sscanf or better yet strtol.
Your code has other issues, detailed in the comments with corrections:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct Student
{
int roll;
char name[50];
int age;
char branch[50];
char gender; //F for female and M for male
};
For solution with scanf only it should, more or less, look like this:
void clear_buffer(){ // helper function to clear buffer
int c;
while((c = getchar()) != '\n' && c != EOF){}
if(c == EOF){
fprintf(stderr, "Fatal error!");
exit(EXIT_FAILURE);
}
}
int main()
{
struct Student s1;
printf("enter roll number of the student: ");
while (scanf("%d", &s1.roll) != 1){
fprintf(stderr, "Bad input, try again: ");
clear_buffer();
} // if bad input ask again
printf("Enter student name: "); // the space before % clears blanks
while (scanf(" %49[^\n]", s1.name) != 1){ // will read the line until
fprintf(stderr, "Bad input, try again: "); // enter is pressed, provided
clear_buffer(); // that it's not larger than 49
}
printf("Enter age number: ");
while(scanf("%d", &s1.age) != 1){
fprintf(stderr, "Bad input, try again: ");
clear_buffer();
}
printf("Enter branch number: ");
while (scanf(" %49[^\n]", s1.branch) != 1){ // branch is a string, %d
clear_buffer(); // specifier is for ints.
fprintf(stderr, "Bad input, try again: "); // note that I'm using width
} // limit (49) to avoid buffer overflow
printf("Enter Gender: ");
while(scanf(" %c", &s1.gender) != 1){ // only 1 character needed, use %c
fprintf(stderr, "Bad input, try again: ");
clear_buffer();
}
}
For a solution with fgets only which, I would argue is better, you can do something like this:
int main(){
struct Student s1;
char temp[50];
printf("enter roll number of the student: ");
if (fgets(temp, sizeof temp, stdin)){
if (sscanf(temp, "%d", &s1.roll) != 1){
fprintf(stderr, "Error parsing input!\n");
}
}
printf("Enter student name: ");
if (fgets(temp, sizeof temp, stdin)){
if (sscanf(temp, "%49[^\n]", s1.name) != 1){
fprintf(stderr, "Error parsing input!\n");
}
}
printf("Enter age number: ");
if (fgets(temp, sizeof temp, stdin)){
if (sscanf(temp, "%d", &s1.age) != 1){
fprintf(stderr, "Error parsing input!\n");
}
}
printf("Enter branch number: ");
if (fgets(temp, sizeof temp, stdin)){
if (sscanf(temp, "%49[^\n]", s1.branch) != 1){
fprintf(stderr, "Error parsing input!\n");
}
}
printf("Enter Gender: ");
if (fgets(temp, sizeof temp, stdin)){
if (sscanf(temp, " %c", &s1.gender) != 1){
fprintf(stderr, "Error parsing input!\n");
}
}
}
*scanf to parse ints still has a potencial flaw in case of overflow, there is no way of guarding against that, unless you use a more robust method like the aforementioned strtol.