Operator '-' cannot be applied to operands of type 'string' and 'int'

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Dear

i have grid view and there is 2 fields with INT value, i want to made '-' operator between them,

i do something like this :

C#

SqlCommand com2 = new SqlCommand("update Book SET (Total) ='" + Convert.ToInt32(g1.Cells[5].Text) - Convert.ToInt32(g1.Cells[4].Text) + "')", con);

when i run the page i got this error:

Operator '-' cannot be applied to operands of type 'string' and 'int'.

both field in DB is INT.

* G1 is gridview name

Posted 20-Sep-14 22:23pm

firas_rehawi

Updated 20-Sep-14 22:28pm

Kornfeld Eliyahu Peter

v2

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Abhinav S · Answer 1 · 2014-09-20T22:37:00

Solution 3

Try this -

string st = string.Format("update Book SET (Total) ='{0}')", (Convert.ToInt32(g1.Cells[5].Text) - Convert.ToInt32(g1.Cells[4].Text))); 
SqlCommand com2 = new SqlCommand(st, con);

Posted 20-Sep-14 22:37pm

Abhinav S

Comments

firas_rehawi 21-Sep-14 7:36am

Thanks But we i complete my statement i got error:
the complete statement is:

string st = string.Format("update Book SET (Total) ='{0}'", (Convert.ToInt32(g1.Cells[5].Text) - Convert.ToInt32(g1.Cells[4].Text)) " where ID = '" + Convert.ToInt32(g1.Cells[0].Text) + "'");
SqlCommand com2 = new SqlCommand(st, con);

com2.ExecuteNonQuery();

and the error is: incorrect syntax near '('. "referring to the ExecuteNonQuery call"

Mehdi Gholam 21-Sep-14 8:43am

5'ed, but the ending paran is extra.

Abhinav S 21-Sep-14 23:09pm

Thanks.

Mehdi Gholam · Answer 2 · 2014-09-20T22:33:00

Solution 1

Put a parenthesis around your computation so the inner value is evaluated correctly then converted to a string for concatenation :

C#

SqlCommand com2 = new SqlCommand("update Book SET (Total) =" + ( Convert.ToInt32(g1.Cells[5].Text) - Convert.ToInt32(g1.Cells[4].Text) ) , con);

Posted 20-Sep-14 22:33pm

Mehdi Gholam

Updated 21-Sep-14 2:41am

v3

Comments

firas_rehawi 21-Sep-14 7:39am

Thanks But we i complete my statement i got error:
the complete statement is:

SqlCommand com2 = new SqlCommand("update Book SET (Total) ='" + (Convert.ToInt32(g1.Cells[5].Text) - Convert.ToInt32(g1.Cells[4].Text)) + " ' " + " where ID = '" + Convert.ToInt32(g1.Cells[0].Text) + "'" , con);

com2.ExecuteNonQuery();

and the error is: incorrect syntax near '('. "referring to the ExecuteNonQuery call"

Mehdi Gholam 21-Sep-14 8:40am

Try the edited version, removed the ending "')" which is not needed.

Kornfeld Eliyahu Peter · Answer 3 · 2014-09-20T22:34:00

You try to concatenate string and int but do not set precedence...
What you try to do is:

C#

"string" + int - int + "string"

The problem is that after the "string" + int part you will get a string, so the next computation is "string" - int, and that can not be done!
Remember that there is no precedence between + and -!!!
You can use parenthesis to solve it, but I advise you to learn about String.Format and about parametrized SQL commands in C# (most important!!!)