possible scanf crash/ auto assigning of values

Question

when running my main function and using scanf to get a char input, my program prints "4227467 device(s) found!" (input 1: 2, input 2:'B') and crashes after that. Wonder if its due to \n or any misunderstanding i may have towards scanf.

int main() {
    int option;
    printf("electronic devicedatabase (EDD)\n1 = Get database information\n2 = Search by port type\n3 = Search by current / power ratings\n=====\nInput: ");
    scanf("%d",&option);

    if (option ==1){
    database_info();

    }
    else if (option == 2){
        char port_type;
        printf("Specify port type: ");
        scanf("%c\n",&port_type);
        search_port_type(port_type);

    }
    else if (option ==3){
        float current_rating, power_rating;
        printf("Specify current and power: ");
        scanf("%f %f\n",&current_rating, &power_rating);
        search_current_power(current_rating, power_rating);

    }
    else{
        printf("Invalid input!\n");
    };
    return 0;
}

void search_port_type(char port_type) {
    int index[5],counter = 0,i = 0;
    for (i=0; i<5; i++){
        if (dev_database[i].port_type == port_type ){
                index[counter]=i;
                counter++;
        }
    }
    printf("%d device(s) found!\n",counter);
    for (i=0; i<counter; i++){
        print_device(index[i]);
    }
    return;
}
void search_current_power(float current, float power) {
    int index[5],counter = 0,i = 0;
    for (i=0; i<5; i++){
        if (dev_database[i].current_rating == current &&  dev_database[i].power_rating == power){
                index[counter]=i;
                counter++;
        }
    }
    printf("%d device(s) found!\n",counter);
    for (i=0; i<counter; i++){
        print_device(index[i]);
    }
    return;
}

Attached is the hyperlink to the full code, ive check each individual function and its working as intended. https://onlinegdb.com/BkGxu3u1z

Any help is greatly appreciated, thank you!

~~Edit: initialised automatic/local variable in the blocks. Option 3 works now! However option 2 still does not work and always give "0 device(s) found!" when giving 'B' as an input.~~

Final edit: Im was wrong with giving 'B' as using scanf("%c\n",&port_type) does not require the ' '.

sample data:

struct device {
    int ports;
    char port_type;
    float cost;
    int cpu_cores;
    int chips;
    struct {
        int version;
        int year;
        char manufacturer[10];
    } make;
    float current_rating, power_rating;
};

struct device dev_database[5] = {
    {5, 'B', 73.45, 4, 7, {2, 2015, "Intel"}, 3.1, 1.2},
    {5, 'A', 70.00, 2, 5, {1, 2010, "Micron"}, 2.0, 1.5},
    {5, 'B', 65.00, 2, 5, {1, 2011, "Intel"}, 3.0, 1.5},
    {5, 'C', 80.00, 8, 7, {1, 2015, "Motorola"}, 2.5, 1.0},
    {5, 'A', 70.00, 2, 5, {3, 2012, "Intel"}, 3.0, 1.3}
};

@Jean-FrançoisFabre hello, i typed 2 for the first scanf for option and 'B' for the second scanf for port_type. — Timothy Teo, Nov 14 '17 at 18:41
You never initialize the `counter` variable to `0` in the functions that print the number of devices found. — Barmar, Nov 14 '17 at 18:42
@user3121023 hi, i tried that method but my program still crashes. — Timothy Teo, Nov 14 '17 at 18:42
Using a debugger you would have discovered both the problems. — Barmar, Nov 14 '17 at 18:43
@Barmar i read online that int variables are automatically initialised as 0, am i wrong? — Timothy Teo, Nov 14 '17 at 18:45
Clearly you're wrong, or you wouldn't be seeing the output you're seeing. Learn to use the debugger. — Ken White, Nov 14 '17 at 18:46
@TimothyTeoChekGuan That's only true for static variables, not automatic variables. — Barmar, Nov 14 '17 at 18:46
@KenWhite im currently using code::block and GDB/CDB default debugger. Is this set-up sufficient to help me debug? — Timothy Teo, Nov 14 '17 at 18:49
If they permit you to step line-by-line through the code as it executes, yes. — Ken White, Nov 14 '17 at 18:50
Note that `scanf()` returns the number of successful assignments made, yet posted code does not check this value in any of the calls to `scanf()`. Check the return value to be sure that input is as expected and to avoid undefined behavior. In general you should check the value returned from _any_ function that returns a meaningful value. — ad absurdum, Nov 14 '17 at 18:56

score 0 · Answer 1 · answered Nov 14 '17 at 19:12

Local/Automatic variables not initialised. Causing inaccuracy in answer. refer to local variable initialized to zero in C

need to add space in front of scanf

updated code:

int main() {
    int option;
    printf("electronic devicedatabase (EDD)\n1 = Get database information\n2 = Search by port type\n3 = Search by current / power ratings\n=====\nInput: ");
    scanf("%d",&option);

    if (option ==1){
    database_info();

    }
    else if (option == 2){
        char port_type;
        printf("Specify port type: ");
        scanf(" %c",&port_type);
        search_port_type(port_type);

    }
    else if (option ==3){
        float current_rating, power_rating;
        printf("Specify current and power: ");
        scanf(" %f %f",&current_rating, &power_rating);
        search_current_power(current_rating, power_rating);

    }
    else{
        printf("Invalid input!\n");
    };
    return 0;
}

void search_port_type(char port_type) {
    int index[5],counter = 0,i = 0;
    for (i=0; i<5; i++){
        if (dev_database[i].port_type == port_type ){
                index[counter]=i;
                counter++;
        }
    }
    printf("%d device(s) found!\n",counter);
    for (i=0; i<counter; i++){
        print_device(index[i]);
    }
    return;
}
void search_current_power(float current, float power) {
    int index[5],counter = 0,i = 0;
    for (i=0; i<5; i++){
        if (dev_database[i].current_rating == current &&  dev_database[i].power_rating == power){
                index[counter]=i;
                counter++;
        }
    }
    printf("%d device(s) found!\n",counter);
    for (i=0; i<counter; i++){
        print_device(index[i]);
    }
    return;
}

possible scanf crash/ auto assigning of values

1 Answers1