Find Sum and Average function not returning actual value of Average

Question

Here's my function that returns the Sum of all pair numbers in an array, and the Average of Odd numbers. Although it outputs the Average as zero for some reason.

 #include <stdio.h>
 
 int MoySom(int Tab[],float* Moyenne,int Length)
 {
     int S=0,C=0;
     *Moyenne=0;
     for(int i=0;i<Length;++i)
     {
         if(Tab[i] % 2 == 0)
         {
             S=S+Tab[i];
         }
         else if(Tab[i] % 2 != 0)
         {
             *Moyenne+=Tab[i];
             ++C;
         }
     }
     *Moyenne=*Moyenne/C;
     return S;
     
 }
 
 void main()
 {
     int Length,Tab[Length];
     float Moyenne;
     printf("Entrer la longeur de tableau: ");
     scanf("%d",&Length);
     for(int i=0;i<Length;++i)
     {
         printf("Entrer l'element %d: ",i);
         scanf("%d",&Tab[i]);
     }
     printf("Somme est:%d\nMoyenne est: %.2f",
         MoySom(Tab,&Moyenne,Length), Moyenne);
 }

There isn't any guarantee that the parameters will be evaluated in a certain order. [Parameter evaluation order before a function calling in C](https://stackoverflow.com/a/376288) — 001, Dec 02 '22 at 19:26
Unless you are on windows main returns an int. How do you expect `int Length, Tab[Length]` to possible work? — Allan Wind, Dec 02 '22 at 19:28
How many elements are in Tab? It is defined before Length is set. — jmq, Dec 02 '22 at 19:30
What is the function supposed to do? If there is no odd numbers in `Tab` then `C` is 0 and you divide by zero. If length is negative or zero your Tab is undefined. — Allan Wind, Dec 02 '22 at 19:36

chux - Reinstate Monica · Accepted Answer · 2022-12-02T19:46:18.187

At least these problems:

Wrong declaration order

int Length,Tab[Length]; is junk. The declaration of Tab[Length] is happening, yet the value of Length is indeterminate.

Something more like the below. Declare Tab[] after Length is assigned.

 int Length;
 float Moyenne;
 printf("Entrer la longeur de tableau: ");
 scanf("%d",&Length);
 int Tab[Length];

Better code checks the return value of scanf()

 int cnt = scanf("%d",&Length);
 if (cnt != 1 || Length <= 0) {
   Report_Error_and_exit();
 } 
 int Tab[Length];

Parameter evaluation order assumed

Calculate Moyenne, then used use it.

//printf("Somme est:%d\nMoyenne est: %.2f",
//     MoySom(Tab,&Moyenne,Length), Moyenne);

printf("Somme est:%d\n", MoySom(Tab,&Moyenne,Length));
printf("Moyenne est: %.2f", Moyenne);

Potential /0

*Moyenne=*Moyenne/C; may attempt divide by zero. Better code would prevent that.

Unneeded test

     if(Tab[i] % 2 == 0) {
       S=S+Tab[i];
     } else if(Tab[i] % 2 != 0) {
       *Moyenne+=Tab[i];

simplifies to

     if(Tab[i] % 2 == 0) {
       S=S+Tab[i];
     } else {
       *Moyenne+=Tab[i];

You can avoid problems like this by always using a single line of code for each declaration. — Robert Harvey, Dec 02 '22 at 19:30

Find Sum and Average function not returning actual value of Average

1 Answers1