A simple "for" command doesnt work using only the stdio library

Question

Using the same machine and IDE as reffered in my other question (third paragraph at Problems in code or my IDE/comp is bugged?)

I try to run this code:

#include <stdio.h>
#define n 3
int main()
{
    int i;
    float values[n],sumval,svmean,tmp;
    for(i=0;i<n;++i)
    {
        scanf("%f",&tmp);
        values[i]=tmp;
        sumval = sumval + values[i];
    }
    svmean = sumval/n;
    printf("%f \n",svmean);
    return(0);
}

The above code is supposed to run this formula

That means that it has to add some values and divide the result by their total number.

As you see above I made an array with random n positions and I ask the user to fill in a value for each position then add them all up and divide them.

The problem is that it doesnt work. It outputs only the result 7 no matter what the iput is.

BUT if I include stdlib.h to the code it works fine.

so

• Question A: why the code does not work properly using only the stdio.h library? which element of the code does require the stdlib.h library?

As you see the array values[n] seems to have an random n number of cells but actually I have already set this numer to be equal to 3 (using #define)

• Question B: Is there a way to run a code with the same porpuse but letting the user to define the size of the array values[n] or in other words let the user input an integer that sets the value of n in values[n]?

Answer 1

First of all, you forgot to initialize sumval. You want it to be 0 at the beginning.

If you want the size of the array to be decided at runtime, you have to allocate it dynamically using malloc, for example like this:

int n;
float *values,sumval=0,svmean,tmp;
scanf("%d", &n);
values = (float *) malloc (n * sizeof(float));

Later, you should release the memory allocated by calling free:

free(values);

Answer 2

Initialize sumVal to o. Because for first iteration it adds garbage+values[i] into sumValue.

 #include <stdio.h>
 #define n 3
 int main()
 {
 int i;
 float values[n],sumval=0,svmean,tmp;
 for(i=0;i<n;++i){
 scanf("%f",&tmp);
 values[i]=tmp;
 sumval = sumval + values[i];
 }
  sumean = sumval/n;
  printf("%f \n",svmean);
  return(0);

}

Answer 3

The problem is that you do not initialize sumval. You should set it to 0.0 before you for loop.

The change occurring when including/not-including stdio.h is probably due to some initialization functions using the stack, and changing the values in memory, before you enter your function, and it happen that this memory is used for your sumval variable.

But you should NOT rely on this.

Answer 4

You can allocate an array with variable size in the heap of the program like that:

#include <stdio.h>
int main(int argc, char **argv)
{
   int i;
   //Get the size of the array from input parameter
   int n = atoi(argv[1]);                
   float sumval,svmean,tmp;
   //Allocate the array of values
   float *values = malloc(sizeof(float)*n);
   // Initialize sumval
   for(sumval=0,i=0;i<n;++i){
      scanf("%f",&tmp);
      values[i]=tmp;
      sumval = sumval + values[i];
   }
   svmean = sumval/n;
   printf("%f \n",svmean);
   //Free it
   free( values );               
   return(0);
  }

You also need to initialize sumval to 0. The parameter of the size of the array is passed when launching the program (if you use an IDE you should check how it does that)

Answer 5

Question A answer In the code you posted there is no need for stdlib.h. This library is needed if you use a function for allocating memory dynamically, such as malloc().

Question B answer: This is a way to do what you want:

#include <stdio.h>

int main()
{
    int i, choice;
    float *values,sumval,svmean,tmp;
    printf("Please enter the size of the array: ");
    scanf("%d", &choice);
    values = (float*) malloc(choice*sizeof(float));
    for(i=0;i<n;i++){
        scanf("%f",&tmp);
        values[i]=tmp;
        sumval = sumval + values[i];
    }
    svmean = sumval/n;
    printf("%f \n",svmean);
    free(values);
    return 0;
}

Also, I modified the incrementation of i in the for statement to increase after running the loop.

Answer 6

Try this..

#include <stdio.h>

int main()
{
    int i = 0;
    int n = 0;
    float sumval = 0;
    float svmean = 0;
    float tmp = 0;

    printf("Enter count : ");
    scanf("%d", &n);

    for (i = 0; i < n; ++i) {
        scanf("%f", &tmp);
        sumval = sumval + tmp;
    }

    svmean = sumval/n;
    printf("%f \n",svmean);

    return(0);
}

In your code, values[] array is not necessary to calculate output. Are you storing the values for any reason??..