This is an extension of rule:

STR30-C. Do not attempt to modify string literals

As string literals are constant, they should only be assigned to constant pointers.

Non-compliant Coding Example 1

The const keyword is not included in these declarations.

char* c1 = "Hello"; // Bad: assigned to non-const
char c2[] = "Hello"; // Bad: assigned to non-const
char c3[6] = "Hello"; // Bad: assigned to non-const
c1[3] = 'a'; // Undefined (but compiles)

Complaint Solution 1

If you properly assign string literals to const pointers, the compiler will not allow direct manipulation of the contents.

char* const c1 = "Hello"; // Good
char const c2[] = "Hello"; // Good
char const c3[6] = "Hello"; // Good
//c1[3] = 'a'; would cause a compile error

Non-compliant Coding Example 2.a

Though it is not compliant with the C Standard, this code executes correctly if the contents of CMUfullname are not modified.

char* CMUfullname = "Carnegie Mellon";

/* get school from user input and validate */

if (strcmp(school,"CMU")) {
    school = CMUfullname;
}

Non-compliant Coding Example 2.b

Adding in the const keyword will generate a compiler warning, as the assignment of CMUfullname to school discards the const qualifier. Any modifications to the contents of scholl after this assignment will lead to errors.

char* const CMUfullname = "Carnegie Mellon";

/* get school from user input and validate */

if (strcmp(school,"CMU")) {
    school = CMUfullname;
}

Compliant Solution 2

The compliant solution uses the const keyword to protect the string literal, as well as using strcpy to copy the value of CMUfullname into school, allowing future modification of school.

char* const CMUfullname = "Carnegie Mellon";

/* get school from user input and validate */

if (strcmp(school,"CMU")) {
    //assuming school is properly allocated above
    strcpy(school, CMUfullname);
}

Risk Assessment

Modifying string literals causes undefined behavior, resulting in abnormal program termination and denial-of-service vulnerabilities.

References:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1993/N0389.asc
[Lockheed Martin 2005] Lockheed Martin. Joint Strike Fighter Air Vehicle C++ Coding Standards for the System Development and Demonstration Program. Document Number 2RDU00001, Rev C. December 2005.     AV Rule 151.1