command gets stuck for some reason - c

Question

I am trying to input basic ip address from the user, but my command gets stuck here in the scanf and nothing after that is executed.
int ip1,ip2,ip3,ip4;
scanf("%d.%d.%d.%d",&ip1,&ip2,&ip3,&ip4);
printf("Here");
So, basically "Here" is never printed and the command scanf never gets over?
#include <stdio.h>
#include<math.h>
int main(void) {
char input;
char rep = 'r';
char quit = 'q';
char first = '1';
char second = '2';
input = rep;
while( input != quit) {
printf("What type of conversion do you want? \n");
printf("Enter 1 for 32-bit number to dot-decimal conversion, 2 for the inverse of operation: ");
char val;
scanf(" %c", &val);
if( val == first) {
} else if( val == second) {
printf("\nEnter dot-decimal IP address:");
int ip1,ip2,ip3,ip4;
scanf(" %d.%d.%d.%d", &ip1,&ip2,&ip3,&ip4);
printf("Here");
unsigned int ip = 0,c,k,counter = 31;
for(c = 7; c >= 0; c--) {
k = ip1 >> c;
if(k & 1) {
int temp = 2,i;
for(i = 0; i < counter;i++) {
temp *= 2;
}
ip += temp;
counter--;
}
}
for(c = 7; c >= 0; c--) {
k = ip2 >> c;
if(k & 1) {
int temp = 2,i;
for(i = 0; i < counter;i++) {
temp *= 2;
}
ip += temp;
counter--;
}
}
for(c = 7; c >= 0; c--) {
k = ip3 >> c;
if(k & 1) {
int temp = 2,i;
for(i = 0; i < counter;i++) {
temp *= 2;
}
ip += temp;
counter--;
}
}
for(c = 7; c >= 0; c--) {
k = ip4 >> c;
if(k & 1) {
int temp = 2,i;
for(i = 0; i < counter;i++) {
temp *= 2;
}
ip += temp;
counter--;
}
}
printf("%u is the IP Address",ip);
}
printf("\n \n Enter r to repeat, q to quit:");
scanf(" %c",&input);
}
return 0;
}
This is the exactly what i was doing. It gets stuck on when i try to get the IP Address in decimal notation.

Answer 1

I have analyzed your code after update (full code) and found that problem not in the input with scanf but in the for loops that are executed after data is obtained.
Look at that loop:
unsigned int ip = 0,c,k,counter = 31;
for(c = 7; c >= 0; c--) {
k = ip1 >> c;
if(k & 1) {
int temp = 2,i;
for(i = 0; i < counter;i++) {
temp *= 2;
}
ip += temp;
counter--;
}
}
and particularly at for(c = 7; c >= 0; c--) taking into account that c is of type unsigned int... I see that this loop is INFINITE because decrement makes from 0 new positive value UINT_MAX (see limits.h).