#include<stdio.h>
int main(){
    int num,r,sum=0,temp;

    printf("Enter a number: ");
    scanf("%d",&num);

    for(temp=num;num!=0;num=num/10){
         r=num%10;
         sum=sum*10+r;
    }
    if(temp==sum)
         printf("%d is a palindrome",temp);
    else
         printf("%d is not a palindrome",temp);

    return 0;
}
Sample output:
Enter a number: 1221
1221 is a palindrome

#include<stdio.h>

int checkPalindrome(int);
int main(){
    int num,sum;

    printf("Enter a number: ");
    scanf("%d",&num);

    sum = checkPalindrome(num);

    if(num==sum)
         printf("%d is a palindrome",num);
    else
    printf("%d is not a palindrome",num);

    return 0;
}

int checkPalindrome(int num){

    static int sum=0,r;

    if(num!=0){
         r=num%10;
         sum=sum*10+r;
         checkPalindrome(num/10);
    }

    return sum;
}
Sample output:
Enter a number: 25
25 is not a palindrome

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

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

 
  printf("Enter a, b and c of quadratic equation: ");
  scanf("%f%f%f",&a,&b,&c);
   
  d = b * b - 4 * a * c;
  
  if(d < 0){
    printf("Roots are complex number.\n");

    printf("Roots of quadratic equation are: ");
    printf("%.3f%+.3fi",-b/(2*a),sqrt(-d)/(2*a));
    printf(", %.3f%+.3fi",-b/(2*a),-sqrt(-d)/(2*a));
  
    return 0; 
  }
  else if(d==0){
   printf("Both roots are equal.\n");

   root1 = -b /(2* a);
   printf("Root of quadratic equation is: %.3f ",root1);

   return 0;
  }
  else{
   printf("Roots are real numbers.\n");
  
   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 a, b and c of quadratic equation: 2 4 1
Roots are real numbers.
Roots of quadratic equation are: -0.293, -1.707

#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;
}