C Programming: Input only integer

Result:

//input number only #include<stdio.h> #include<conio.h> #include<stdlib.h> int InputINT(); void main() { int math,physic,english; printf("math: "); math=InputINT(); printf("physic: "); physic=InputINT(); printf("english: "); english=InputINT(); printf("Average = %.2f",(math+physic+english)/3.0); } int InputINT() { int num,i=0; char st[20]=""; char ch; ch=getch(); while(ch!=13) { if(ch>=48&&ch<=57) { printf("%c",ch); st[i]=ch; i=i+1; } if(ch==8&&i>0) { printf("\b"); i=i-1; st[i]='\0'; } ch=getch(); } num=atoi(st); printf("\n"); return(num); }