cannot convert char to char & illegal use of floating point - c

Question

Below is a simple program that the user enters the number of subjects taken --> the grade (A,B,C etc.) --> and the program calculates and prints the students transcript including all the cgpa.
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char string[10];
char grade[10];
float out[10];
int num;
float cgpa=0.0;
for(int x=0;x<num;x++)
{
printf("\nEnter the number of subjects? \n ");
scanf("%d",&num);
printf("\nEnter Student Name: \n");
scanf("%s",&string[x]);
printf("\nEnter Student Grade: \n");
scanf("%s",&grade[x]);
if(grade[x]>="A" || grade[x]>="a")
out[x]==4.0;
else if(grade[x]>="B" || grade[x]>="b")
out[x]==3.0;
else if(grade[x]>="C" || grade[x]>="c")
out[x]==2.0;
else if(grade[x]>="D" || grade[x]>="d")
out[x]==1.3;
else if(grade[x]>="F" || grade[x]>="f")
out[x]==0.1;
else
printf("You've entered a wrong grade");
}
cgpa+=out;
cgpa=cgpa/num;
printf("%s\n", string);
printf("%s\n", grade);
printf("%f\n", cgpa);
getch();
}
My main problem is that I keep on getting the two following errors:
Cannot convert char to char*
illegal use of floating point
The errors I'm getting are on the following lines:
if(grade[x]>="A" || grade[x]>="a")
out[x]==4.0;
else if(grade[x]>="B" || grade[x]>="b")
out[x]==3.0;
else if(grade[x]>="C" || grade[x]>="c")
out[x]==2.0;
else if(grade[x]>="D" || grade[x]>="d")
out[x]==1.3;
else if(grade[x]>="F" || grade[x]>="f")
out[x]==0.1;
The illegal use of floating point error is on this line:
cgpa+=out;

Answer 1

Please see solution. Your original solution had a lot of issues and is fundamentally flawed. The above commentary highlight most of the mistakes you've made, but the main flaw with your original solution was the lack of clear process structure.
Recommend drafting out your algorithm or process flow before you begin coding in future
1. Grab user input for student name and number of subjects
2. For every subject
a. Get user to input grade
b. Check grade is valid
c. Add to cumulative GPA value
Until num_subjects is met
3. Print out Student Name, Num Subjects and his GPA (cgpa/num_subjects)
See sample solution below, which adheres to the process I defined above.
I hope this assists you in your programming journey :)
#include <stdio.h>
// #include <conio.h> - Commented this out because this is MS Dos specific and makes solution non portable
#include <ctype.h>
int main(void)
{
int num_subjects;
char name[10];
char grade;
float cgpa=0.0;
int x;
// These do not need to be within your loop. Especially num_subjects
printf("\nEnter Student Name: \n");
scanf("%s", &name[0]);
printf("\nEnter the number of subjects? \n ");
scanf("%d", &num_subjects);
// I've replaced this with a while loop, because you need a continuous loop until a valid grade is required
while( x < num_subjects )
{
printf("\nEnter Student Grade: \n");
scanf("%c", &grade);
// Upper case the value, so there is no ambiguity in 'a' or 'A'
grade = toupper(grade);
printf("\nGrade Entered: %c\n", grade);
if (grade == 'A') {
cgpa+=4.0;
}
else if (grade == 'B') {
cgpa+=3.0;
}
else if (grade == 'C') {
cgpa+=2.0;
}
else if (grade == 'D') {
cgpa+=1.3;
}
else if (grade == 'F') {
cgpa+=0.1;
}
else {
printf("You've entered a wrong grade");
// Being lazy here. I'm decrementing the counter, because I am lazy.
// By right, the efficient thing to do is to increment the counter on a valid value
// But in the interest of writing less code, I've decided to decrement the value on an invalid value.
// And add more comments :P
x--;
}
// Increment x if a valid grade was entered.
x++;
}
// Final output line
printf("\nStudent: %s, Number Subjects: %d, GPA: %.2f", name, num_subjects, cgpa/num_subjects);
}

Answer 2

You can't add a whole array to a floating point number.
And grade [x] is a char while "A" is a char array.
Also you have to scanf your number before using it in your for loop.

Answer 3

Change this:
if(grade[x]>="A" || grade[x]>="a")
out[x]==4.0;
For this:
if(grade[x]>='A' || grade[x]>='a')
out[x]=4.0;
Why?
reason 1: grade is an array of characters, not strings.
reason 2: == is a boolean operator (like the >= in your example). To set a variable value use just =
Study a little before coding. It is a very basic question.