Student Management system using c language

Below is the complete code.

To compile & play with it online use link: https://www.programiz.com/online-compiler/3ENxYbYvXkt5Z

#include <stdio.h>
#include <string.h>
struct studentstruct {
  int rollnum;
  char stdname[50];
  int stdmarks;
  char stdgrade[3];
};
struct studentstruct students[100];
int student_count = 0;
int uschoice, a;
void addStudent();
void mainmenu();
int std_count = 0;
int b;
int nmb_std;
int roll_srch, find_roll,srch_choice;
char name_srch[50];





void addStudent(int index) {
  if (student_count == 100) {
    printf("Storage full! Cannot add more students.\n");
    a = 1;

    mainmenu();

  } else {
    b = 1;
    printf("Enter Roll Number: ");
    scanf("%d", &students[index].rollnum);
    if (students[index].rollnum > 10000000) {
      printf("Only include integers!");
    }
    printf("Enter Name: ");
    scanf(" %[^\n]", students[index].stdname);

    printf("Enter Marks (0-100): ");
    scanf("%d", &students[index].stdmarks);
    if (students[index].stdmarks > 100) {
      printf("Marks more than 100!");
    }
    printf("Enter Grade: ");
    scanf(" %2s", students[index].stdgrade);
    student_count++;
    mainmenu();
  }
}

void showstudent(int index) {
  if (student_count == 0) {
    printf("No students to display.\n");
    return;
  }

  printf("\n--- Student Record ---\n");
  printf("Roll: %d\n", students[index].rollnum);
  printf("Name: %s\n", students[index].stdname);
  printf("Marks: %d\n", students[index].stdmarks);
  printf("Grade: %s\n", students[index].stdgrade);
  mainmenu();
}

void mainmenu() {
  printf("<----MAIN MENU---->\n");
  printf("1.Add record\n");
  printf("2.Display record\n");
  printf("3.Search record\n");
  printf("4.Exit\n");
  printf("Enter your choice:");
  scanf("%d", &uschoice);
  if (uschoice == 1) {
    if (a == 1) {
      student_count = 100;
    }
    if (b == 1) {
      std_count++;
    }
    addStudent(std_count);
  }

  if (uschoice == 2) {
          printf("Enter Name:");
      scanf(" %[^\n]", name_srch);
    
      int found = 0;
      for (int i = 0; i < student_count; i++) {
        if (strcmp(students[i].stdname, name_srch) == 0) {
          showstudent(i);
          found = 1;
        }
      }
      if (found == 0) {
        printf("Student with name %s not found.\n", name_srch);
        mainmenu();
      }
  }






  if (uschoice == 3) {
    printf("[1]Search with Roll no\n[2]Search with name\nEnter your choice here:");
    scanf("%d", &srch_choice);
    if(srch_choice==1){
    
      printf("Enter Roll no:");
      scanf("%d", &roll_srch);
    
      int found = 0;
      for (int i = 0; i < student_count; i++) {
        if (students[i].rollnum == roll_srch) {
          showstudent(i);
          found = 1;
        }
      }
      if (found == 0) {
        printf("Student with roll %d not found.\n", roll_srch);
        mainmenu();
      }
    } else {
      
      printf("Enter Name:");
      scanf(" %[^\n]", name_srch);
    
      int found = 0;
      for (int i = 0; i < student_count; i++) {
        if (strcmp(students[i].stdname, name_srch) == 0) {
          showstudent(i);
          found = 1;
        }
      }
      if (found == 0) {
        printf("Student with name %s not found.\n", name_srch);
        mainmenu();
      }
    } 
  }   

  if (uschoice == 4) printf("Thanks for using my app!");
} 

int main() {
  mainmenu();
  return 0;
}