Infinite loop when trying to count letter frequencies - c

Question

#include <stdio.h>
#include <string.h>
int main(void)
{
char string[100];
int c = 0, count[26] = {0};
int accum = 0;
int a;
while(1)
{
a = scanf("%s", string);
while ( string[c] != '\0' )
{
if ( string[c] >= 'a' && string[c] <= 'z' ){
count[string[c]-'a']++;
accum++;
}
else if (string[c] >= 'A' && string[c] <= 'Z'){
count[string[c]-'A']++;
accum++;
}
c++;
}
if (a == EOF)
{
for ( c = 0 ; c < 26 ; c++ )
{
if( count[c] != 0 )
printf( "%c %f\n", c+'a', ((double)count[c])/accum);
}
}
}
return 0;
}
So I have a program that counts the frequencies of letters that appear in standard input until EOF. But once I reach EOF, my program just goes into an infinite loop and the frequencies doesn't seem to be right. When I just put a print statement to enter a single string, it works fine. I don't really know what the problem is. Would anybody be able to help me with this?

Answer 1

if (a == EOF) should be right after a = scanf("%s", string);
Then that if() condition should exist the loop.
Should reset c = 0 each time in loop
while(1) {
a = scanf("%s", string);
if (a == EOF) {
...
break;
}
c = 0;
while ( string[c] != '\0' ) {
With the above changes, confident your code will run fine. There are other things to consider on lesser degree. 1) The scanf("%s",... is unbounded. 2) Should limit input. if (a == EOF) might as well code after the loop. 3) Suggest the loop condition is the positive affirmation that scanf()==1. Loop on what is good, not exit on a case of what is bad. 4) Consider unsigned vs. int for counting. 5) A for() loop rather than while() is nice for incremental loops. 6) Avoid magic numbers like 26.
BTW: Your code had nice use of casting for floating point, A literals and array {0} initialization.
#include <stdio.h>
#include <string.h>
int main(void) {
char string[100];
unsigned count['z' - 'a' + 1] = { 0 };
unsigned accum = 0;
while (scanf("%99s", string) == 1) {
for (int c = 0; string[c]; c++) {
if (string[c] >= 'a' && string[c] <= 'z') {
count[string[c] - 'a']++;
accum++;
} else if (string[c] >= 'A' && string[c] <= 'Z') {
count[string[c] - 'A']++;
accum++;
}
}
}
for (int c = 'a'; c <= 'z'; c++) {
if (count[c - 'a'] != 0)
printf("%c %f\n", c, ((double) count[c - 'a']) / accum);
}
return 0;
}

Answer 2

The infinite loop is caused by this line:
while(1)
Remove it if you don't need it, or add a break statement somewhere.

Answer 3

Some more words to help describe your problem and the solution (as proposed by chux).
The first problem that you have is that you have no logic to exit the while(1) loop.
IE you have an infinite loop because that is what you have coded.
Even though you detect the EOF, you don't do anything about it: there is nothing in your code that says "Now that we have EOF, we need to exit this while(1) loop".
This is what chux is suggesting in his answer: that is what the break statement is for: it says "break out of the loop now".
You also have an additional problem that you are parsing the string before you check if you have EOF. If a is EOF, then you must not parse the string, because you didn't get one.
So you need to rearrange your code so that your EOF check is before your string parsing, and when you finish printing the string after detecting EOF, you need to break.