最大值始终设置为8

Question

I was writing a program that takes the input, and then prints the maximum value of the frequency of each letter in it. For this program, I have decided to take the input only as these 5 letters: a,b,c,d and e. The program goes like this.

#include <stdio.h>

int main(){
    int i, c , nchar[5];
    int maxvalue;

   for(i=0;i<5;i++){
    nchar[i]=0;
   }

    /*COLLECTING AND SETTING THE DATA*/
    while((c=getchar())!=EOF){
        if (c=='a')
            nchar[0]++;

        else if (c=='b')
            nchar[1]++;

        else if (c=='c')
            nchar[2]++;

        else if (c=='d')
            nchar[3]++;

        else if (c=='e')
            nchar[4]++;

    }
    printf("%d",setMax(nchar,maxvalue));


}
int setMax(int a[5], int maxv){
    if ( a[0]> a[1] &&  a[0]> a[2] &&  a[0]>a[3] &&  a[0]> a[4])
        a[0]=maxv;

    else if ( a[1]> a[0] && a[1]> a[2] && a[1]> a[3] && a[1]> a[4])
        a[1]=maxv;

    else if ( a[2]> a[0] && a[2]> a[1] && a[2]> a[3] && a[2]> a[4])
        a[2]=maxv;

    else if ( a[3]> a[0] && a[3]> a[2] && a[3]> a[1] && a[3]> a[4])
        a[3]=maxv;

    else if ( a[4]> a[0] && a[4]> a[2] && a[4]> a[3] && a[4]> a[1])
        a[4]=maxv;

        return maxv;

}

Now, for example I write the input as 'aaabc', it should print the value 3 because the maximum frequency is of letter 'a' which is 3. But, it is printing the value 8. Not only this input, but anything I write as input, it always prints 8. Can someone tell me what mistake have I done?

Answer 1

You have your logic backward.

Instead of

if ( a[0]> a[1] &&  a[0]> a[2] &&  a[0]>a[3] &&  a[0]> a[4])
    a[0]=maxv;

you need

if ( a[0]> a[1] &&  a[0]> a[2] &&  a[0]>a[3] &&  a[0]> a[4])
    maxv = a[0];

General Improvement

Change the name of the function setMax() to getMax() and change its signature to:

int getMax(int a[5]);

Change the usage to:

printf("%d", getMax(nchar);

And change the implementation to:

int getMax(int a[5]){

   int maxv = 0;
    if ( a[0]> a[1] && a[0]> a[2] &&  a[0]>a[3] &&  a[0]> a[4])
        maxv = a[0];

    else if ( a[1]> a[0] && a[1]> a[2] && a[1]> a[3] && a[1]> a[4])
        maxv = a[1];

    else if ( a[2]> a[0] && a[2]> a[1] && a[2]> a[3] && a[2]> a[4])
        maxv = a[2];

    else if ( a[3]> a[0] && a[3]> a[2] && a[3]> a[1] && a[3]> a[4])
        maxv = a[3];

    else if ( a[4]> a[0] && a[4]> a[2] && a[4]> a[3] && a[4]> a[1])
        maxv = a[4];

    return maxv;
}

Update

An updated version of getMax() that fixes the problem when two values are equal.

int getMax(int a[5])
{
   if ( a[0] >= a[1] && a[0] >= a[2] &&  a[0] >= a[3] &&  a[0] >= a[4] )
      return a[0];

   // a[0] is not the max. it has has be a[1], a[2], a[3], or a[4]
   if ( a[1] >= a[2] && a[1] >= a[3] && a[1] >= a[4] )
      return a[1];

   // Similarly, the max has to be a[2], a[3], or a[4]
   if ( a[2] >= a[3] && a[2] >= a[4] )
      return a[2];

   // Similarly, the max has to be a[3] or a[4]
   if ( a[3] >= a[4] )
      return a[3];

   // At this point, a[4] has to be the max value.
   return a[4];
}

Answer 2

do maxval = 0 and just return a[0] a[1] etc which ever condition is satisfied. Dont assign the value to maxval.

Or if you want to do like this, Here is the code for setMax() func:

int setMax(int a[5], int maxv){

int i=0;
maxval = a[0];
for (i=1;i<5;i++)
 if (maxval < a[i])
  maxval = a[i];
return maxval;
}

Answer 3

The variable maxvalue has an undefined value when you call setMax() .

This gives undefined behavior.

Also I don't think setMax() makes sense. I think it should do return a[0] in the first if , and so on.

Answer 4

The variable maxvalue is uninitialized, and it's value will be indeterminate. Using it in calculations will lead to undefined behavior.

Besides, you always return it (or rather maxv ) from the setMax function without modifications , so you will always print the same value.

Answer 5

As already pointed my Mr. Unwind and Mr. JP, the usage of maxvalue in current code invokes undefined behaviour , as you're using an uninitialized automatic variable value.

Based on the usage of setMax() function in your code, I think, what you want to do is (are)

• Point 1 You don't need to define maxvalue in main() and pass that as a parameter to setMax() .

• Point 2 Inside setMax() function, define a local maxvalue and change a[0]=maxv; and series to maxv = a[0]; and likewise.