As been mentioned in the comments, this is not a trivial task that could be written with a few lines of code. What you need is a parser. That parser needs to handle many different cases. Here is a (probably non-exhaustive) list:
- One line comments:
// This is a comment
- Multiline comments:
/* This is a comment */
- Characters:
char c='&'
- String literals:
strcmp(str, "A string with a & in it")
- The bitwise operator:
int a = mask & b
You would also need to decide how to handle incorrect input. Should the program be able to detect incorrect c code, or should it assume all input is correct? Another thing to consider is how to handle #include. Do you want to count the number of occurrences in the included files too? (I assume not, but this demonstrates a problem)
If you want it to 100% accurate in finding only the address operator, then it is way above your knowledge. (OP wrote "This is a problem is designed to be solved by 1st-semester students with only basic knowledge." in comment below)
If you're allowed to cut some corners there are easier ways.
Here is a complete example that cut some corners. It handles comments and strings, including escaped characters. However, it does not handle the bitwise operator.
#include <stdio.h>
#include <stdlib.h>
#define INPUT "input.c"
int main()
{
FILE *f;
if ((f = fopen(INPUT, "r")) == NULL)
{
perror (INPUT);
return (EXIT_FAILURE);
}
char c, p=0;
int n=0;
while((c = fgetc(f)) != EOF)
{
if(c == '/' && p == '/') {
while((c = fgetc(f)) != EOF) {
// If we read // then we throw away the rest of the line
if( c == '\n' ) {
break;
}
}
if( c == EOF) {
goto end;
}
}
else if(c == '*' && p == '/') {
// If we read /* then we throw away everything until we have read */
while((c = getc(f)) != EOF) {
if( c == '*' ) {
if((c = getc(f)) != EOF)
if( c == '/')
break;
}
} if ( c == EOF) {
goto end;
}
}
else if(c == '"') {
// Read until end of string
while((c = getc(f)) != EOF) {
if(c == '\\') {
if((c = getc(f)) == EOF)
goto end;
}
else if(c == '"')
break;
}
}
else if(c == '\'') {
while((c = getc(f)) != EOF) {
if(c == '\\') {
if((c = getc(f)) == EOF)
goto end;
}
else if(c == '\'')
break;
} if ( c == EOF)
goto end;
}
else if(c == '&') {
printf("hej");
if(p == '&')
n--;
else
n++;
}
p=c;
}
end:
printf("\n\nExited at pos %ld\n", ftell(f));
printf("Number of address operators: %d\n", n);
}
It works a bit like this: When it sees a start of a comment, it reads and throws away everything until the comment is finished or EOF. It does the same for strings.
On this input:
// Test &
/* Also
&
test */
// "
int main()
{
/* " //
*/
// /*
char str[]="hej&\"";
char c='&';
char k='\'';
int a, b;
int * p;
p=&a;
int c=a&b;
int q=a&&b;
}
// Test &
/* Also
&
test */
It reports the expected result 2. It would be better if it printed 1, but as I mentioned, it cannot handle the bitwise operator, thus counting it as an address operator. Fixing this issue would make things a lot more complicated.
And yes, I'm using goto since it is extremely convenient in a situation like this. In C++, I'd use exceptions, but that's not an option in C.
