C Prime Check Product or Sum

#include<stdio.h> 
#include<stdlib.h> 
int count_sum = 0; 
int count_product = 0; 
int check_sum_prime(int num); 
int check_product_prime(int num); 
int check_digit(int num); 
int check_sum_prime(int num) 
{ 
int rem=0; 
int mult = 0; 
int final = 0; 
while(num!=0) 
{ 
rem=num%10; 
mult+=rem; 
num=num/10; 
} 
if(check_digit(mult) != 1) 
{ 
check_sum_prime(mult); 
} 
else if(check_digit(mult) == 1) 
{ 
if(mult==2 || mult==3 || mult==5 || mult==7 ) 
{ 
count_sum++; 
} 
} 
} 
int check_product_prime(int num) 
{ 
int rem=0; 
int mult = 1; 
int final = 0; 
while(num!=0) 
{ 
rem=num%10; 
mult*=rem; 
num=num/10; 
} 
if(check_digit(mult) != 1) 
{ 
check_product_prime(mult); 
} 
else if(check_digit(mult) == 1) 
{ 
if(mult==2 || mult==3 || mult==5 || mult==7 ) 
count_product++; 
} 
} 
int check_digit(int num) 
{ 
int count=0,rem1; 
while(num!=0) 
{ 
rem1=num%10; 
count++; 
num/=10; 
} 
return count; 
} 
main() 
{ 
do 
{ 
int choice; 
int i; 
int upper_limit,lower_limit; 
printf("\n\n********** MENU **********\n"); 
printf("\n1. Check Product Prime."); 
printf("\n2. Check Sum Prime."); 
printf("\n3. EXIT."); 
printf("\nEnter Your Choice:"); 
scanf("%d",&choice); 
switch(choice) 
{ 
case 1: 
count_product = 0; 
printf("\n********** Check Product Prime **********\n\n"); 
printf("Enter the Range:-----"); 
printf("\n\nLower Limit: "); 
scanf("%d",&lower_limit); 
printf("\nUpper Limit: "); 
scanf("%d",&upper_limit); 
for(i=lower_limit;i<=upper_limit;i++) 
check_product_prime(i); 
printf("\nNumber of Sum Primes between %d and %d = %d",lower_limit,upper_limit,count_product); 
break; 
case 2: 
count_sum = 0; 
printf("\n********** Check Sum Prime **********\n\n"); 
printf("Enter the Range:-----"); 
printf("\n\nLower Limit: "); 
scanf("%d",&lower_limit); 
printf("\nUpper Limit: "); 
scanf("%d",&upper_limit); 
for(i=lower_limit;i<=upper_limit;i++) 
check_sum_prime(i); 
printf("\nNumber of Sum Primes between %d and %d = %d",lower_limit,upper_limit,count_sum); 
break; 
case 3: 
printf("\nThanks Friend for checking my code....\n"); 
exit(0); 
default: 
printf("\nPlease give a valid choice\n"); 
} 
}
while(1); 
}