#include<stdio.h>
float add(float,float);
float sub(float,float);
float product(float,float);
float divide(float,float);
void main()
{
float n1,n2;
char sym,choice;
printf("This Program is a program for calculator\n\n");
scanf("%f%c%f",&n1,&sym,&n2);
if(sym=='+')
printf("\n%f",add(n1,n2));
if(sym=='-')
printf("\n%f",sub(n1,n2));
if(sym=='*')
printf("\n%f",product(n1,n2));
...