Function average and stdDev const int tab[ ]. Average problems - c

Question

I have to use:
float average(const int tab[], int size);
float stdDev(const int tab[], int size);
to printf average and stdDev in C.
I have problem with average and i think with const int.
When i add const int tab[101] i have error with a1;
So how can i make it work with const int (if i can).
And if it is anything wrong with this code.
Any help will be helpful.
#include<stdio.h>
#include<math.h>
float average(const int tab[], int size);
float stdDev(const int tab[], int size);
int main()
{
float ave, std;
int a1;
int j;
int tab[101];
printf("Podaj liczby: ");
for(j=0; j<=99; j++)
{
a1 = scanf("%d", &tab[j]);
if(a1<1)
{
printf("Incorrect input");
return 1;
}
if(tab[0]==0)
{
printf("not enough data available");
return 2;
}
if(tab[j]==0)
{
break;
}
}
ave = average(tab, j);
printf("%.2f\n", ave);
std = stdDev(tab, j);
printf("%.2f", std);
return 0;
}
float average(const int tab[], int size)
{
int i;
float y=0, x;
if(size<=0)
{
return -1;
}
for(i=0; i<size; i++)
{
x = x + tab[i];
}
y = x/size;
return y;
}
float stdDev(const int tab[], int size)
{
int i;
float y, z, z1, z2=0, z3=0;
if(size<=0)
{
return -1;
}
y = average(tab, size);
for(i=0; i<size; i++)
{
z = tab[i] - y;
z1 = pow(z, 2);
z2 = z2 + z1;
z=0;
z1=0;
}
z3 = sqrt(z2/size);
return z3;
}

Answer 1

You define the variable x in average here:
float y=0, x;
without giving it a value. Then here:
x = x + tab[i];
you are reading its value without setting it anywhere beforehand. Because you never gave x a value, its value will be indeterminate and reading it will cause undefined behavior, which means that your program could e.g. print garbage output.
Always initialize your variables:
float y=0, x=0;