CODEWITHSUNDEEP
cfunctionpointers
ArtisticMelody
ArtisticMelody

Reputation: 63

Passing value by pointer

As far as I'm concerned I'm passing the variables spoilt and valid through to the function Proccosvotes correctly, but I'm not getting the right answer. Instead of incrementing valid by 1 like I thought I was doing, it's adding random numbers to it. For instance, I should be getting around 200 for valid, but I'm getting 2687468. I can seem to find the error. Does anyone see or know the mistake I'm making?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct election{
    char name[20];
    int votes;
};

struct election electionCandidates[7];

void Initialize(struct election electionCandidates[], int num, FILE *ifp);
void Processvote(struct election electionCandidates[], int num, FILE *ifp, int *valid1, int *spoilt1);

int main(){
    FILE *ifp;
    char *winner[20]; 
    int valid = 0;
    int spoilt = 0;
    int num;

    ifp = fopen("elections.txt", "r"); 

    Initialize(electionCandidates, 6, ifp);

    Processvote(electionCandidates, 6, ifp, &valid, &spoilt); 

    system("PAUSE");

    printResults(electionCandidates, 6, &valid, &spoilt, *winner); 


    printf("GO");
    system("PAUSE");

    fclose(ifp);

    system("PAUSE");
    return 0;
}

void Initialize(struct election *electionCandidates, int num, FILE *ifp){
    int i = 0;
    for(i=0; i<7; i++){
        fscanf(ifp, "%[^\n]%*c", &electionCandidates[i].name);
        printf("%d: %s\n", i, electionCandidates[i].name);
    }
}

void Processvote(struct election *electionCandidates, int num, FILE *ifp, int *valid1, int *spoilt1){
    int i;
    int x=0;
    int j;
    for(i=0; i<365; i++){
        fscanf(ifp, "%d ", &x);

        for(j=1; j<=7; j++){
            if (j == x){
                electionCandidates[j].votes+=1;
                valid1++;
            }  

            if (x < 1 || x > 7)
                spoilt1++;                  
        }
        printf("valid: %d\nspoilt: %d\n", valid1, spoilt1);
    }  
}

Upvotes: 0

Views: 527

Answers (2)

Bill Lynch
Bill Lynch

Reputation: 81996

Problem 1

In C, arrays start counting at 0 not 1.

Therefore, the following code will cause undefined behavior, because you call electionCandidates[7].

    for(j=1; j<=7; j++){
        if (j == x){
            electionCandidates[j].votes+=1;

Problem 2

spoilt1 and valid1 are pointers to single integers. If you want to use the value that the pointer is pointing to, then you should do things like:

printf("%d", *spoilt1);
*spoilt1 += 1;

Problem 3

You're missing the implementation of printResults(), so I'm not sure how you're running this at all.

Problem 4

Your compiler should be printing out a few warnings for this code. At the very least, you should fix them. Note that warnings are often indicative of a real problem in your code that you shouldn't ignore. Here's the warnings and errors that my compiler reports:

[11:53am][wlynch@watermelon /tmp] clang foo.c
foo.c:30:5: warning: implicit declaration of function 'printResults' is invalid in C99 [-Wimplicit-function-declaration]
    printResults(electionCandidates, 6, &valid, &spoilt, *winner); 
    ^
foo.c:45:34: warning: format specifies type 'char *' but the argument has type 'char (*)[20]' [-Wformat]
        fscanf(ifp, "%[^\n]%*c", &electionCandidates[i].name);
                     ~~~~        ^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:66:43: warning: format specifies type 'int' but the argument has type 'int *' [-Wformat]
        printf("valid: %d\nspoilt: %d\n", valid1, spoilt1);
                       ~~                 ^~~~~~
foo.c:66:51: warning: format specifies type 'int' but the argument has type 'int *' [-Wformat]
        printf("valid: %d\nspoilt: %d\n", valid1, spoilt1);
                                   ~~             ^~~~~~~
4 warnings generated.
Undefined symbols for architecture x86_64:
  "_printResults", referenced from:
      _main in foo-1d49c9.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Problem 5

You should check that your calls to fscanf() actually succeed. If the file is short or otherwise invalid, you might not update the value of your variables.

Upvotes: 2

thurizas
thurizas

Reputation: 2528

In Processvote, valid1 has the type pointer to an integer. In you code you write valid1++, which is incrementing the value of the pointer, not what it is pointing to. Try (*valid1)++ and also (*spoilt1)++

Upvotes: 0

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