The invalid choice in the code appears in the output screen - c

Question

Why does the "Invalid" appear in my output under everything? The invalid choice is the last thing in the menu, am I'm using the statement right or what exactly is wrong?
#include <stdio.h>
void two_assesments();
void three_assesments();
void four_assesments();
void five_assesments();
void six_assesments();
int main( void )
{
int c;
printf("\n*****Student Grade Calculator*****\n\n");
printf(" Developed By...\n");
printf(" Carlos\n");
printf(" University of South Wales\n");
printf(" =================================================================\n");
printf("\n");
printf("\n Please enter the number of assessments in the module : \n");
scanf("%d",&c);
if (c==2) {
two_assesments();
}
if (c==3) {
three_assesments();
}
if (c==4) {
four_assesments();
}
if (c==5) {
five_assesments();
}
if (c==6) {
six_assesments();
}
else
if (c=!7); {
{ printf("\nInvalid"); }
}
return(0);
}

Answer 1

The problem is here
else
if (c=!7); { . . .
You have a ; after if ()
I would suggest you use a switch statement like this
switch (c) {
case 2: two_assesments(); break;
case 3: three_assesments(); break;
case 4: four_assesments(); break;
case 5: five_assesments(); break;
case 6: six_assesments(); break;
default: printf("\nInvalid\n");
}
to make your code more readable.

Answer 2

To understand the problem, consider what happens if the user enters 2. The first if statement evaluates true and the two_assesments function is called. The next three if statements fail. Then we get to the if (c==6). That also fails, so the else is evaluated. And here you have two problems.
First is the semi-colon. Because you have a semicolon after the if (c=!7) the compiler sees your code as
if (c==6) {
six_assesments();
}
else {
if (c=!7)
; /* do nothing */
}
printf("\nInvalid");
In other words, because of the semicolon, the final if statement has no effect, and the printf isn't even part of the else. So "Invalid" always gets printed.
The other problem is the =!. What you meant to say was if (c!=7). By reversing the = and the !, you actually assign 0 to c, and the if always evaluates to false. The compiler should be giving you a warning about that.
A slightly improved version of the code would look like this
if (c==2)
two_assesments();
else if (c==3)
three_assesments();
else if (c==4)
four_assesments();
else if (c==5)
five_assesments();
else if (c==6)
six_assesments();
else
printf("\nInvalid");