i have a program in c that finds the first and second max in an array, but i want to get the indexes of these elements. Here is my code:
#include <stdio.h>
int main(){
int max1,max2,n;
scanf("%d",&n);
int a[n],i;
int i_m1,i_m2;
i_m1 = i_m2=0;
for(i = 0;i < n;i ){
scanf("%d",&a[i]);
}
max1 = max2 = 0;
for(i = 0;i < n;i ){
if(a[i]>max1){
max1=a[i];
//i_m1 ;
} else if(a[i]>max2 && a[i]<max1){
max2=a[i];
//i_m2 ;
}
}
printf("%d %d\n",max1,max2);
//printf("%d %d\n",i_m1,i_m2);
for(i = 0;i < n;i ){
printf("%d ",a[i]);
}
return 0;
}
I first enter the number of elements in the array then the array.
For example if i have an array
number of elements: 5
elements in array:
3 4 2 5 1
indexes:
0 1 2 3 4
max1=5, max2=4
i_m1=3, i_m2=1
How can i get the indexes i_m1 and i_m2 ?
CodePudding user response:
You're thinking too hard about what to do with i
as evidenced by the commented out i_m1
and i_m2
.
If max1=a[i];
then it follows that i_m1 = i;
and same for max2
/i_m2
.
CodePudding user response:
For starters even this if-else statement
for(i = 0;i < n;i ){
if(a[i]>max1){
max1=a[i];
//i_m1 ;
} else if(a[i]>max2 && a[i]<max1){
max2=a[i];
//i_m2 ;
}
}
is wrong.
If the condition of the if statement
if(a[i]>max1){
is true then you need also assign max1
to max2
if max1
is not equal to max2
before changing max1
.
The approach can look the following way
if ( n < 2 )
{
i_m1 = 0;
i_m2 = 0;
}
else
{
if ( a[0] < a[1] )
{
i_m1 = 1;
i_m2 = 0;
}
else
{
i_m1 = 0;
i_m2 = 1;
}
for ( i = 2; i < n; i )
{
if ( a[i_m1] < a[i] )
{
if ( a[i_m2] < a[i_m1] ) i_m2 = i_m1;
i_m1= i;
}
else if ( a[i_m2] < a[i] )
{
i_m2 = i;
}
}
}
printf( "max1 = %d max2 = %d\n", a[i_m1], a[i_m2] );
printf( "i_m1 = %d i_m2 = %d\n", i_m1, i_m2 );
Here is a demonstration program.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main( void )
{
enum { N = 10 };
int a[N];
int n = N;
srand( ( unsigned int )time( NULL ) );
for ( int i = 0; i < n; i )
{
a[i] = rand() % N;
}
for ( int i = 0; i < n; i )
{
printf( "%d ", a[i] );
}
putchar( '\n' );
// Below the algorithm for a variable length array
int i_m1 = 0, i_m2 = 0;
if ( !( n < 2 ) )
{
if ( a[0] < a[1] )
{
i_m1 = 1;
i_m2 = 0;
}
else
{
i_m1 = 0;
i_m2 = 1;
}
for ( int i = 2; i < n; i )
{
if ( a[i_m1] < a[i] )
{
if ( a[i_m2] < a[i_m1] ) i_m2 = i_m1;
i_m1= i;
}
else if ( a[i_m2] < a[i] )
{
i_m2 = i;
}
}
}
printf( "max1 = %d max2 = %d\n", a[i_m1], a[i_m2] );
printf( "i_m1 = %d i_m2 = %d\n", i_m1, i_m2 );
}
Its output might .look like
0 3 5 0 3 8 8 2 5 6
max1 = 8 max2 = 8
i_m1 = 5 i_m2 = 6
CodePudding user response:
Also logic error.
Once a new max1
found, the old value should become the new max2
.
if(a[i]>max1){
max2 = max1; // add
max1 = a[i];
} else if(a[i]>max2 && a[i]<max1){
max2=a[i];
}