Problem with specific command

**Muppetlol** · 05-15-2012

Code:

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

void main(void)
{
    //declaration
    int Np00000, Ns00000;
    float Vp00000, Vs00000;
    char A, B, C, D, reply;

    //intialization
    printf("A : Primary Voltage");
    printf("\nB : Secondary Voltage");
    printf("\nC : Number of Primary windings/coils");
    printf("\nD : Number of Secondary windings/coils");

    printf("\n\nWhich of the above component are you finding?(A , B , C or D) : ");
    scanf("%c",&reply);

    if (reply == "A")
    {
    printf("This program calculates the Primary Voltage(Vp) of a transformer");
    printf("\nEnter the number of coils in the Primary(Np): ");
    scanf("%d", &Np00000);
    printf("\n\nEnter the number of coils in the Secondary(Ns): ");
    scanf("%d", &Ns00000);
    printf("\nEnter the voltage in the Secondary (in Volts): ");
    scanf("%f", &Vs00000);
    

    //calculation

    Vp00000 =  Np00000 * Vs00000 / Ns00000;

    //output
    printf("\n\nThe Primary Voltage(Vs) is %.2f V", Vp00000);
    }//end of A

    if (reply == "B")
    {
    printf("This program calculates the Secondary Voltage (Vs) of a transformer"); 
    printf("\nEnter the number of turns in the Secondary(Ns): ");
    scanf("%d", &Ns00000);
    printf("\n\nEnter the number of turns in the Primary(Np): ");
    scanf("%d", &Np00000);
    printf("\nEnter the voltage in the primary winding(Vp) (in Volts): ");
    scanf("%f", &Vp00000);

    //calculation

    Vs00000 =  Ns00000 * Vp00000 / Np00000;

    //output
    printf("\n\nThe Secondary Voltage(Vs) is %.2f V", Vs00000);
    }//end of B

    if (reply == "C")
    {
    printf("This program calculates the number of Primary winding/coils of a transformer"); 
    printf("\n\nEnter the voltage in the Primary winding(Vp) (in Volts): ");
    scanf("%f", &Vp00000);
    printf("\nEnter the number of turns in the Secondary winding/coils: ");
    scanf("%d", &Ns00000);
    printf("\nEnter the voltage in the Secondary winding/coils(Vs) (in Volts): ");
    scanf("%f", &Vs00000);

    //calculation

    Np00000 = Ns00000 * Vp00000 / Vs00000;

    //output
    printf("\n\nThe number of Primary turn is %d", Np00000);
    }

    exit(0);

}

Currently I have this problem at the part of declaring with character A B C or D at the start. For example when I press B , it doesn't go to the if (reply == "B") part of the program , instead it starts with the if (reply == "A") part , causing my whole program about calculating transformer voltage and number of coils to be wrong.

I know its the part of my declaring that is causing the mistake but I'm clueless about how exactly am i suppose to declare it.

Hope someone can give me some advice

**Salem** · 05-15-2012

Use single quotes, for single letters.

You should be getting compiler warnings when you use double quotes.

Also, main returns an int, not void.

**ledow** · 05-15-2012

Code:

reply == "A"

This innocent-looking statement is incredibly wrong. "A" is actually a string consisting of the A character and a null return. Comparing strings using == only compares the pointer (i.e. the memory location of those strings). So unless reply is in the same part of memory as A (not just having the same content), it will return a bad answer. You probably want to use single quotes ('A') which means to compare against a specific CHARACTER (because that's what you read in from scanf).

To compare strings you require the strcmp functions.

P.S. Enabling your warnings helps immensely and is said SO OFTEN on these forums that I get bored of keep saying it:

Code:

gcc -O3 -g3 -Wall -c -fmessage-length=0 -otest.o ..\test.c
..\test.c:5: warning: return type of 'main' is not 'int'
..\test.c: In function 'main':
..\test.c:21: warning: comparison between pointer and integer
..\test.c:21: warning: comparison with string literal results in unspecified behavior
..\test.c:40: warning: comparison between pointer and integer
..\test.c:40: warning: comparison with string literal results in unspecified behavior
..\test.c:58: warning: comparison between pointer and integer
..\test.c:58: warning: comparison with string literal results in unspecified behavior
..\test.c:10: warning: unused variable 'D'
..\test.c:10: warning: unused variable 'C'
..\test.c:10: warning: unused variable 'B'
..\test.c:10: warning: unused variable 'A'

As you can see, there are also lots of other problems with your code too.

**Muppetlol** · 05-15-2012

Sorry I just start C Programming like a month ago so I'm still unsure about the usage of some commands like the one you said about single quotes. Do I just change void main(void) to int main(void)?? Otherwise what should I do, cause I'm just starting the chapter on branching using "if" and "else". If possible can someone show me a paragraph of commands that will allow me to correct my mistakes

**stahta01** · 05-15-2012

FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com

**claudiu** · 05-15-2012

What ledow was saying is that 'C' is different from "C", the first is a character, the second is a string containing a single character. (ie you would write "ABC", not 'ABC')

In your code you want to compare the character to another character not to a string, and as previously stated == is not used for string comparison anyway, the function strcmp() is.

**Muppetlol** · 05-15-2012

so i did a small change and it ended up like this

Code:

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

void main(void)
{
    //declaration
    int Np00000, Ns00000;
    float Vp00000, Vs00000;
    char A, B, C, D, reply;

    //intialization
    printf("A : Primary Voltage");
    printf("\nB : Secondary Voltage");
    printf("\nC : Number of Primary windings/coils");
    printf("\nD : Number of Secondary windings/coils");

    printf("\n\nWhich of the above component are you finding?(A , B , C or D) : ");
    scanf("%c",&reply);

    if (reply == 'A')
    {
    printf("\nThis program calculates the Primary Voltage(Vp) of a transformer.");
    printf("\n\nEnter the number of coils in the Primary(Np): ");
    scanf("%d", &Np00000);
    printf("\n\nEnter the number of coils in the Secondary(Ns): ");
    scanf("%d", &Ns00000);
    printf("\nEnter the voltage in the Secondary (in Volts): ");
    scanf("%f", &Vs00000);
    

    //calculation

    Vp00000 =  Np00000 * Vs00000 / Ns00000;

    //output
    printf("\n\nThe Primary Voltage(Vs) is %.2f V.", Vp00000);
    }//end of A

    if (reply == 'B')
    {
    printf("\nThis program calculates the Secondary Voltage (Vs) of a transformer."); 
    printf("\nEnter the number of turns in the Secondary(Ns): ");
    scanf("%d", &Ns00000);
    printf("\n\nEnter the number of turns in the Primary(Np): ");
    scanf("%d", &Np00000);
    printf("\nEnter the voltage in the primary winding(Vp) (in Volts): ");
    scanf("%f", &Vp00000);

    //calculation

    Vs00000 =  Ns00000 * Vp00000 / Np00000;

    //output
    printf("\n\nThe Secondary Voltage(Vs) is %.2f V.", Vs00000);
    }//end of B

    if (reply == 'C')
    {
    printf("\nThis program calculates the number of Primary winding/coils of a transformer."); 
    printf("\n\nEnter the voltage in the Primary winding(Vp) (in Volts): ");
    scanf("%f", &Vp00000);
    printf("\nEnter the number of turns in the Secondary winding/coils: ");
    scanf("%d", &Ns00000);
    printf("\nEnter the voltage in the Secondary winding/coils(Vs) (in Volts): ");
    scanf("%f", &Vs00000);

    //calculation

    Np00000 = Ns00000 * Vp00000 / Vs00000;

    //output
    printf("\n\nThe number of Primary turn(s) is %d.", Np00000);
    }//end of C

    if (reply == 'D')
    {
    printf("\nThis program calculates the number of Secondary winding/coils of a transformer."); 
    printf("\n\nEnter the voltage in the Secondary winding(Vs) (in Volts): ");
    scanf("%f", &Vs00000);
    printf("\nEnter the number of turns in the Primary winding/coils: ");
    scanf("%d", &Np00000);
    printf("\nEnter the voltage in the Primary winding/coils(Vs) (in Volts): ");
    scanf("%f", &Vp00000);

    //calculation

    Ns00000 = Np00000 * Vs00000 / Vp00000;

    //output
    printf("\n\nThe number of Secondary turn(s) is %d.", Ns00000);
    }//end of D

    exit(0);

}

Looks like the program is working fine now

**laserlight** · 05-15-2012

That is good to hear. One thing you can do to improve your code is to indent it better. You have one level of indentation in the main function, but the code within the body of each if statement should be indented by another level.

You should specify the return type of main to be int, not void. Instead of exit(0) at the end of main, just use return 0;

Also, since you are not using the char variables named A, B, C and D, you should remove their declarations. Then, it may make more sense to rename Vp00000 to just Vp or better yet, primary_voltage (or something like that). If you do need more such variables later, chances are you would be using an array so the 00000 is pointless.

**Muppetlol** · 05-16-2012

I wasn't taught to use int as main and return 0

But its pretty nice to see someone from the same country as me , Singapore , who is able to help me out. Thanks anyway (:

**QuantumPete** · 05-16-2012

Originally Posted by Muppetlol

I wasn't taught to use int as main and return 0

You've been taught to now...

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