# C program to perform intersection operation on two arrays

## Intersection operation

If array 1 = { 1,2,3,4,6}

Array 2 = {1,2,5,6,7}

Then, intersection of array1 and array 2 is

Array1 ^ array 2 = {1,2,3,4,6} ^ {1,2,5,6,7}
= {1,2,6}

Set of common elements is called an intersection.

The logic for intersection is as follows −

k=0;
for(i=0;i<size1;i++){
for(j=0;j<size2;j++){
if(a[i]==b[j]){
intersection[k]=a[i];
k++;
}
}
}

## Program

Following is the C program to perform intersection operation on two arrays −

Live Demo

#include<stdio.h>
int removerepeated(int size,int a[]);
void sort(int size,int a[]);
main(){
int i,size1,size2,size,j=0,k,intersectionsize;
printf("Enter size of an array1");
scanf("%d",&size1);
printf("Enter size of an array2");
scanf("%d",&size2);
int a[size1],b[size2],uni[size1+size2];
if(size1<size2){
intersectionsize=size1;
}else if(size1>size2){
intersectionsize=size2;
}else{
intersectionsize=size1;
}
int intersection[intersectionsize];
printf("Enter numbers for array 1");
for(i=0;i<size1;i++){
scanf("%d",&a[i]);
}
printf("Enter numbers for array 2");
for(i=0;i<size2;i++){
scanf("%d",&b[i]);
}
//Intersection starts
k=0;
for(i=0;i<size1;i++){
for(j=0;j<size2;j++){
if(a[i]==b[j]){
intersection[k]=a[i];
k++;
}
}
}
//Sorting
sort(k,intersection);
//Removing
size=removerepeated(k,intersection);
printf("Array after intersection");
if(size>0){
for(i=0;i<size;i++){
printf("%d",intersection[i]);
}
}else{
printf("No intersection");
}
}
int removerepeated(int size,int a[]){
int i,j,k;
for(i=0;i<size;i++){
for(j=i+1;j<size;){
if(a[i]==a[j]){
for(k=j;k<size;k++){
a[k]=a[k+1];
}
size--;
}else{
j++;
}
}
}
return(size);
}
void sort(int size,int a[]){
int i,j,temp;
for(i=0;i<size;i++){
for(j=i+1;j<size;j++){
if(a[i]>a[j]){
temp=a[i];
a[i]=a[j];
a[j]=temp;
}
}
}
}

## Output

When the above program is executed, it produces the following result −

Enter size of an array1
5
Enter size of an array2
2
Enter numbers for array 1
4
5
6
7
8
Enter numbers for array 2
4
1
Array after intersection
4