Why are my while loops not working? I m getting no error, but also no output.

Codes are working perfectly fine uptil the main logic.

example my output for binary search is : Enter the array size: 5

Enter array elements in sorted form : 1 2 3 4 5 Enter the target element: 2

//no output is shown after this user input (NOTE: Same logics are perrfectly working with for loops)

//Code for Binary search (while loop not working )

#include<stdio.h>
#define max 20
int main(){

    int a[max],n,i,target;
    int l=0;
    int r=n-1;
    int mid=(l r)/2;

    printf("\nEnter the array size: \n");
    scanf("%d",&n);

    printf("\nEnter array elements in sorted form : \n");
    for(i=0;i<n;i  ){
        scanf("%d",&a[i]);
    }
    printf("Enter the target element: ");
    scanf("%d",&target);

while(l<=r){
    
        if(target==a[mid]){
            printf("Element found at %d position",i 1);

        }
        else if(target<a[mid]){
            r=mid-1;
        }
        else{
            l=mid 1;
        }
    
}

return 0;
}

//Same problem with linear search while loop

#include<stdio.h>
#define max 20
int main(){

    int array[max],target,size,i=0,flag=0;
    printf("Enter the size of array: ");
    scanf("%d",&size);
    printf("Enter the elements of array: ");
    for(i=0;i<size;i  ){
        scanf("%d",&array[i]);
    }
    printf("Enter the element to be found in array: ");
    scanf("%d",&target);

    printf("Target accepted");

   while( i < size ) {
      if(array[i]==target){
        printf("Element found at %d position",i 1);
        flag=1;
        break;
      }
      else{
        flag=0;
      }
      i  ;
   }
    if(flag==0){
        printf("Element not found !!!");
    }
    
    return 0;
}

CodePudding user response：

In the while (l<=r) loop, either 'l' or 'r' value is changed, but mid is never changed, thus if(target==a[mid]) will always false.

You need to change 'mid' value in the while loop.

CodePudding user response：

First you were initializing the right index before getting the size of the array so you will never enter the while loop. Second thing is that you should set the middle element inside your while loop so it can update properly every time you change the left and right variables. check the code below:

int a[max],n,i,target;
    int l=0;

    printf("\nEnter the array size: \n");
    scanf("%d",&n);
    int r=n-1;

    printf("\nEnter array elements in sorted form : \n");
    for(i=0;i<n;i  ){
        scanf("%d",&a[i]);
    }
    printf("Enter the target element: ");
    scanf("%d",&target);

    while(l<=r){
    
        int mid=(l r)/2;
        if(target==a[mid]){
            printf("Element found at %d position",mid);
            break;
        }
        else if(target<a[mid]){
            r=mid-1;
        }
        else{
            l=mid 1;
        }