Switch statement using string on an array

Question

#include<stdio.h>

int main(){

    char name[20];

    printf("enter a name ");
    scanf("%s",name);
    switch(name[20]){
        case "kevin" : 
        printf("hello");
        break;
    }
    printf("%s",name);
    getch();
}

It seems it will not work. Is this possible? I mean is there any way we can make a switch statement of a string. How to solve the problem, actually?

Answer 1

Switch statements in C aren't smart like one's found in other languages (such as Java 7 or Go) you cannot switch on a string (Nor can you compare strings with ==). Switch can only operate on integral types (int, char, etc).

In your code you call switch with: switch(name[20]). That means switch(*(name + 20)). In other words switch on the 21st char in name (because name[0] is the first). As name only has 20 chars you are accessing whatever memory is after name. (which could do unpredictable things)

Also the string "kevin" is compiled to a char[N] (where N is strlen("kevin") + 1) which contains the string. When you do case "kevin". It will only work if name is in the exact same piece of memory storing the string. So even if I copied kevin into name. It still would not match as it is stored in a different piece of memory.

To do what you seem to be trying you would do this:

#include <string.h>
...
    if (strcmp(name, "kevin") == 0) {
        ...
    }

String compare (strcmp) returns different values based on the difference in the strings. Eg:

int ord = strcmp(str1, str2);
if (ord < 0)  
    printf("str1 is before str2 alphabetically\n");
else if (ord == 0) 
    printf("str1 is the same as str2\n");
else if (ord > 0)  
    printf("str1 is after str2 alphabetically\n");

Side note: Dont use scanf("%s", name) in that form. It creates a common security problem use fgets like this: (there is a safe way to use scanf too)

#define MAX_LEN 20
int main() { 
    char name[MAX_LEN]; 
    fgets(name, MAX_LEN, stdin);
    ...

Answer 2

Switch statements work on int values (or enum), but not on char arrays.

You could do

if (strcmp(name, "kevin")==0) {
    printf("hello");
}
else if (strcmp(name, "Laura")==0) {
    printf("Allo");
}
else if (strcmp(name, "Mike")==0) {
    printf("Good day");
}
else  {
    printf("Help!");
}