firstly your logic to compute Area is wrong.
secondly printf("The side of square : %d "); requires two parameter , like printf("The side of square : %d ",k);
third error is Area=(SquareArea(k)); you are passing garbage value.
fourth :
for (i=5;i<k;i+=5)
{
printf("The side of square : %d ");
scanf("%d",&k);
A=i*i;
}
is wrong , SquareArea funtion can simply return k*k;
fifth this line scanf("%d",&k); should be in main() before call to SquareArea()