warning: assignment makes pointer from integer without a cast [-Wint-conversion]
warning: return makes integer from pointer without a cast [-Wint-conversion]

    #include<stdio.h>  

    long int jumlah(long int a,long int b, long int * sum){
        sum = (a b);
        return (sum);
    }

    int main(){
        long int a,b,sum;
        scanf("%d %d",&a,&b);
        sum = jumlah(a,b,&sum);
        printf("%d\n",sum);
        return 0;
    }

My program works fine but everything inside the function gets a warning and I want to know why

CodePudding user response：

In the jumlah function you have to dereference the sum pointer to access the variable it points to. The format specifier for long ints is "%ld".

#include <stdio.h>

long int jumlah(long int a, long int b, long int *sum)
{
    *sum = a b;
    return *sum;
}

int main(void)
{
    long int a, b, sum;
    scanf("%ld %ld", &a, &b);
    sum = jumlah(a, b,&sum);
    printf("%ld\n", sum);
    return 0;
}

CodePudding user response：

long int jumlah(long int a,long int b, long int * sum){
    sum = (a b);
    return (sum);
}

sum is a pointer to long int. You can only assign values of type pointer to long int to it. (a b) does return a value of type long int, in order to assign the result to sum, you first have to dereference it, like this: *sum = (a b);

The function return type is long int, but again sum is a pointer type, it makes a huge difference if you return either sum or *sum, one will be an address, the other the value stored at that address.

Either change the return type of that function to long int* and return sum (only if you want to return the address instead the value - but it does not seem like that) or return the value by dereferencing *sum from the function.

CodePudding user response：

As I wrote in the comment under you question, you have mistakenly used the pointer sum as a long int storage type.

This is needlessly complicated. Let's simplify it. (Good code is sharp.)

long int jumlah( long int a, long int b ) {
    return a   b;
}

int main(){
    long int a, b;

    // make use of return values from system (input) functions
    if( scanf( "%d %d", &a, &b ) == 2 )
        printf( "%d\n", jumlah( a, b ) );
    else
        printf( "Input error\n" );

    return 0;
}

CodePudding user response：

Your program may work as expected, but you’re stuffing a long integer into a pointer to long (sum), not AT the pointer to long. Wrong type, but it just happens to fit. Basically, you’re using the sum parameter as a locally defined variable, similar to this:

long int jumlah(long int a,long int b){
long int sum;

sum = a   b;
return (sum);

}

In the main(), since you store the return from jumlah() back into sum, passing &sum doesn’t do much instead of providing that ersatz local variable. If you wanted to store the result at sum (in addition to returning it), jumlah() should be:

long int jumlah(long int a,long int b, long int * sum){
*sum = a   b;
return (*sum);

}

Always treat compiler warnings as errors and fix ‘em.