C GUB Grading using Switch Case

#include <stdio.h>

int main()
{
    int n;
    scanf("%d",&n,printf("Enter your marks:\t"));

    float m = (float)n/10;
    switch(n/10)
    {

        case 8:
        case 9:
        case 10:
            if(n<=100) printf("A+\n");
            break;
        case 7:
            if(m>=7.5 && m<8) printf("A\n");
            else printf("A-\n");
            break;
        case 6:
            if(m>=6.5 && m<7) printf("B+\n");
            else printf("B\n");
            break;
        case 5:
            if(m>=5.5 && m<6) printf("B-\n");
            else printf("C+\n");
            break;
        case 4:
            if(m>=4.5 && m<5) printf("C\n");
            else printf("D\n");
            break;

        default :
            printf("F\n");
            break;
    }

    main();
}