Question:Sum of 1 + 2 + ….  + n series in c programming language 

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

    int n,i;
    int sum=0;

    printf("Enter the n i.e. max values of series: ");
    scanf("%d",&n);

    sum = (n * (n + 1)) / 2;

    printf("Sum of the series: ");

    for(i =1;i <= n;i++){
         if (i!=n)
             printf("%d + ",i);
         else
             printf("%d = %d ",i,sum);
         }
   
    return 0;
}
Sample output:
Enter the n i.e. max values of series: 5
Sum of the series: 1 + 2 + 3 + 4 + 5 = 15

Question:Sum of 1^2 + 2^2 + …. + n^2 series in c programming language 

#include<stdio.h>

int main(){

    int n,i;
    int sum=0;

    printf("Enter the n i.e. max values of series: ");
    scanf("%d",&n);

    sum = (n * (n + 1) * (2 * n + 1 )) / 6;

    printf("Sum of the series : ");

    for(i =1;i<=n;i++){
         if (i != n)
             printf("%d^2 + ",i);
         else
             printf("%d^2 = %d ",i,sum);
    }

    return 0;
}
Sample output:
Enter the n i.e. max values of series: 5
Sum of the series: 1^2 + 2^2 + 3^2 + 4^2 + 5^2 = 55

Question:Write a c program or code to find out the sum of series 1^3 + 2^3 + …. + n^3 that is sum of cube of n natural numbers. 

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

int main(){

    int n,i;
    int sum=0;

    printf("Enter the n i.e. max values of series: ");
    scanf("%d",&n);

    sum = pow(((n * (n + 1) ) / 2),2);

    printf("Sum of the series : ");

    for(i =1;i<=n;i++){
         if (i != n)
             printf("%d^3 + ",i);
         else
             printf("%d^3 = %d ",i,sum);
    }

    return 0;
}
Sample output:
Enter the n i.e. max values of series: 3
Sum of the series: 1^3 + 2^3 + 3^3 = 36

Question:Write a c program to find out the sum of in A.P. series 

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

int main(){

    int a,d,n,i,tn;
    int sum=0;

    printf("Enter the first number of the A.P. series: ");
    scanf("%d",&a);

    printf("Enter the total numbers in the A.P. series: ");
    scanf("%d",&n);

    printf("Enter the common difference of A.P. series: ");
    scanf("%d",&d);

    sum = ( n * ( 2 * a + ( n -1 ) * d ) )/ 2;
    tn = a + (n-1) * d;
    printf("Sum of the series A.P.: ");

    for(i=a;i<=tn; i= i + d ){
         if (i != tn)
             printf("%d + ",i);
         else
             printf("%d = %d ",i,sum);
    }

    return 0;
}
Sample output:
Enter the first number of the A.P. series: 1
Enter the total numbers in the A.P. series: 5
Enter the common difference of A.P. series: 3
Sum of the series: 1 + 4 + 7 + 10 + 13 = 35

Question:Sum of GP series in c programming language 

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

int main(){

    float a,r,i,tn;
    int n;
    float sum=0;

    printf("Enter the first number of the G.P. series: ");
    scanf("%f",&a);

    printf("Enter the total numbers in the G.P. series: ");
    scanf("%d",&n);

    printf("Enter the common ratio of G.P. series: ");
    scanf("%f",&r);

    sum = (a*(1 - pow(r,n+1)))/(1-r);
       tn = a * (1 -pow(r,n-1));

    printf("tn term of G.P.: %f",tn);
    printf("\nSum of the G.P.: %f",sum);

    return 0;
}
Sample output:
Enter the first number of the G.P. series: 1
Enter the total numbers in the G.P. series: 5
Enter the common ratio of G.P. series: 2
tn term of G.P. : 16.000000
Sum of the G.P. : 63.000000

Question:Sum of infinite GP series in c programming language 

#include<stdio.h>

int main(){

    float a,r;
    float sum=0;

    printf("Enter the first number of the G.P. series: ");
    scanf("%f",&a);

    printf("Enter the common ratio of G.P. series: ");
    scanf("%f",&r);

    if(1 > r)
         sum = a/(1-r);
    else
         sum = a/(r-1);

    printf("\nSum of the infinite G.P. series: %f",sum);

    return 0;
}
Sample output:
Enter the first number of the G.P. series: 1
Enter the common ratio of G.P. series: .5

Sum of the infinite G.P. series: 2.000000

Enter the first number of the G.P. series: 5
Enter the common ratio of G.P. series: 2

Sum of the infinite G.P. series: 5.000000

Question:C program to find the largest element in an array 

#include<stdio.h>
int main(){
  int a[50],size,i,big;
  printf("\nEnter the size of the array: ");
  scanf("%d",&size);
  printf("\nEnter %d elements in to the array: ”, size);
  for(i=0;i<size;i++)
      scanf("%d",&a[i]);
  big=a[0];
  for(i=1;i<size;i++){
      if(big<a[i])
           big=a[i];
  }
  printf("\nBiggest: %d",big);
  return 0;
}

Question:C program to find the second largest element in an array 

#include<stdio.h>
int main(){
  int a[50],size,i,j=0,big,secondbig;
  printf("Enter the size of the array: ");
  scanf("%d",&size);
  printf("Enter %d elements in to the array: ", size);
  for(i=0;i<size;i++)
      scanf("%d",&a[i]);
 
  big=a[0];
  for(i=1;i<size;i++){
      if(big<a[i]){
           big=a[i];
           j = i;
      }
  }

  secondbig=a[size-j-1];
  for(i=1;i<size;i++){
      if(secondbig <a[i] && j != i)
          secondbig =a[i];
  }
  
  printf("Second biggest: %d", secondbig);
  return 0;
}
Sample output:
Enter the size of the array: 5
Enter 5 elements in to the array: 5 3 2 1 0
Second biggest: 3

Question:C program to find the second smallest element in an array 

#include<stdio.h>
int main(){
  int a[50],size,i,j=0,small,secondsmall;
  printf("Enter the size of the array: ");
  scanf("%d",&size);
  printf("Enter %d elements in to the array: ", size);
  for(i=0;i<size;i++)
         scanf("%d",&a[i]);

  small=a[0];
  for(i=1;i<size;i++){
         if(small>a[i]){
               small=a[i];
               j = i;
      }
  }

  secondsmall=a[size-j-1];
  for(i=1;i<size;i++){
         if(secondsmall > a[i] && j != i)
              secondsmall =a[i];
  }

  printf("Second smallest: %d", secondsmall);
  return 0;
}
Sample Output:
Enter the size of the array: 5
Enter 5 elements in to the array: 5 7 3 2 6
Second smallest: 3

Question:REMOVE DUPLICATE ELEMENTS IN AN ARRAY USING C PROGRAM 

#include<stdio.h>
int main(){
  int arr[50];
  int *p;
  int i,j,k,size,n;
  printf("\nEnter size of the array: ");
  scanf("%d",&n);
  printf("\nEnter %d elements into the array: ",n);
  for(i=0;i<n;i++)
    scanf("%d",&arr[i]);
  size=n;
  p=arr;
  for(i=0;i<size;i++){
    for(j=0;j<size;j++){
         if(i==j){
             continue;
         }
         else if(*(p+i)==*(p+j)){
             k=j;
             size--;
             while(k < size){
                 *(p+k)=*(p+k+1);
                 k++;
              }
              j=0;
          }
      }
  }
  printf("\nThe array after removing duplicates is: ");
  for(i=0;i < size;i++){
    printf(" %d",arr[i]);
  }
  return 0;
}