简体   繁体   中英

My gcc compiler gives me an, error that shows as Conflicting types for (function)

I'm new to C and i made this program and i'm getting an error "conflicting types for (function)" "previous declaration of (function) was here".

I compiled this using gcc compiler of Dev c++ using command prompt on my system. Can anyone help me understand my fault here ?

#include<stdio.h>
#include<math.h>
main()
{
    int a,b,c;
    float area;
    float ar(int a,int b,int c);
    printf("Enter the lenghts of the three sides of a triangle");
    scanf("%d%d%d",&a,&b,&c);
    area=ar(a,b,c);
    printf("The are a of the triangle is=%.2f",area);
}
ar(a,b,c)
{
    float area,s;
    s=(a+b+c)/3;
    area=sqrt((s*(s-a)*(s-b)*(s-c)));
    return area;
}

You declared your function "ar" with return type float but float ar(int a,int b,int c); but you defined it with no return value.That rised a problem here. try this:

    #include<stdio.h>
    #include<math.h>
    float ar(int a,int b,int c);

    void main()
    {
        int a,b,c;
        float area;
        printf("Enter the lenghts of the three sides of a triangle");
        scanf("%d%d%d",&a,&b,&c);
        area=ar(a,b,c);
        printf("The are a of the triangle is=%.2f",area);
    }
    float ar(int a,int b,int c)
    {
        float area,s;
        s=(a+b+c)/3;
        area=sqrt((s*(s-a)*(s-b)*(s-c)));
       return area;
   }

Compile with the command :gcc -std=c99 -o stack_16_4_16 stack_16_4_16.c -lm

The problem is that you specify a return type in your prototype but not in the actual function definition. When you write the prototype with a particular definition you must follow that same definition when writing the actual function.

I've also cast the integer addition into a float so that you can properly calculate the area. When you take an integer and divide it by a float in C you will end up with an integer regardless of what you are assigning it into. The cast will change this behavior.

Consider this:

#include<stdio.h>
#include<math.h>
int main()
{
    int a,b,c;
    float area;
    float ar(int a,int b,int c);
    printf("Enter the lenghts of the three sides of a triangle");
    scanf("%d%d%d",&a,&b,&c);
    area=ar(a,b,c);
    printf("The are a of the triangle is=%.2f",area);
}
float ar(int a,int b,int c)
{
    float area,s;
    s=(float)(a+b+c)/3;
    area=sqrt((s*(s-a)*(s-b)*(s-c)));
    return area;
}

This will compile cleanly.

I tried to include a bit of explanation here :

#include<stdio.h>
#include<math.h>

float ar(int a,int b,int c); 
/*  This is a function declaration and just like variables, functions are
 *  also limited by scope. If you declare the function inside the main,
 *  then the function cannot be called outside the main. That is the purpose
 *  it is declared here.
 */

int main()
{
    int a,b,c;
    float area;

    printf("Enter the lengths of the three sides of a triangle : ");
    scanf("%d%d%d",&a,&b,&c);
    area=ar(a,b,c);
    printf("The are a of the triangle is = %.2f",area);

    return 0;
}

    float ar(int a,int b,int c)  
    /* Note that I have added the types of arguments
     * In older versions of C it is not uncommon to see functions like 
     * float ar(a,b)
     * int a,b;
     * {Some Stuff Here}
     * The above function style was problematic - it couldn't deal with mismatched arguments.
     * So it is a good practice to specify the type of the parameters.
     * In fact this was ANSI C standard's solution to the problems of mismatched arguments.
     */
    {
    float area,s;
    s=(a+b+c)/(float)2;  
    /* Either the numerator or the denominator  should be float for the output to be float
     * So I casted the denominator to a float value. Also, if you're using Heron's formula
     * the denominator should be 2 , not 3.
     */

    area=sqrt(s*(s-a)*(s-b)*(s-c));

    return area;
    }

You should add a return type to your function ar

#include<stdio.h>
#include<math.h>
main()
{
    int a,b,c;
    float area;
    float ar(int a,int b,int c);
    printf("Enter the lenghts of the three sides of a triangle");
    scanf("%d%d%d",&a,&b,&c);
    area=ar(a,b,c);
    printf("The are a of the triangle is=%.2f",area);
}
float ar(float a, float b, float c)
{
    float area,s;
    s=(a+b+c)/3;
    area=sqrt((s*(s-a)*(s-b)*(s-c)));
    return area;
}

The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.

 
粤ICP备18138465号  © 2020-2024 STACKOOM.COM