#include<stdio.h>
#include<math.h>

int main(){
  float a,b,c;
  float d,root1,root2;  

  printf("Enter quadratic equation in the format ax^2+bx+c: ");
  scanf("%fx^2%fx%f",&a,&b,&c);
   
  d = b * b - 4 * a * c;
  
  if(d < 0){
    printf("Roots are complex number.\n");
   
    return 0;
  }
 
   root1 = ( -b + sqrt(d)) / (2* a);
   root2 = ( -b - sqrt(d)) / (2* a);
   printf("Roots of quadratic equation are: %.3f , %.3f",root1,root2);

  return 0;
}
Sample output:
Enter quadratic equation in the format ax^2+bx+c: 2x^2+4x+-1
Roots of quadratic equation are: 0.000, -2.000

#include<string.h>
#include<stdio.h>
int main(){
  char *str,*rev;
  int i,j;
  printf("\nEnter a string:");
  scanf("%s",str);
  for(i=strlen(str)-1,j=0;i>=0;i--,j++)
      rev[j]=str[i];
      rev[j]='\0';
  if(strcmp(rev,str))
      printf("\nThe string is not a palindrome");
  else
      printf("\nThe string is a palindrome");
  return 0;
}

#include<stdio.h>
int main(){
    int k,r;
    long int i=0l,j=1,f;

    //Taking maximum numbers form user
    printf("Enter the number range:");
    scanf("%d",&r);

    printf("FIBONACCI SERIES: ");
    printf("%ld %ld",i,j); //printing firts two values.

    for(k=2;k<r;k++){
         f=i+j;
         i=j;
         j=f;
         printf(" %ld",j);
    }
  
    return 0;
}
Sample output:
Enter the number range: 15
FIBONACCI SERIES: 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

#include<stdio.h>
int main(){

    int i,range;
    long int arr[40];

    printf("Enter the number range: ");
    scanf("%d",&range);

    arr[0]=0;
    arr[1]=1;

    for(i=2;i<range;i++){
         arr[i] = arr[i-1] + arr[i-2];
    }

    printf("Fibonacci series is: ");
    for(i=0;i<range;i++)
         printf("%ld ",arr[i]);
  
    return 0;
}
Sample output:
Enter the number range: 20
Fibonacci series is: 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181

#include<stdio.h>
int main(){
    int k=2,r;
    long int i=0l,j=1,f;

    printf("Enter the number range:");
    scanf("%d",&r);

    printf("Fibonacci series is: %ld %ld",i,j);

    while(k<r){
         f=i+j;
         i=j;
         j=f;
         printf(" %ld",j);
          k++;
    }
  
    return 0;
}
Sample output:
Enter the number range: 10
Fibonacci series is: 0 1 1 2 3 5 8 13 21 34