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C LAB WORKSHEET 8
C & C++ Selection: if, if-else, if-else-if Part 1
Items in this page:
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The C & C++ conditional statement, a selection.
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The if, if-else construct and flowcharts
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Activities, questions and answers.
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Tutorial reference that should be used together with this worksheet are: C & C++ program control 1 and C & C++ program control 2.
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In this lab worksheet we will deal wit another C/C++ program control, a selection. The if, if-else construct and its variation used in C/C++ when we need to make a selection from the given options based on the certain condition. For example:
if (x == 3)
printf("The if condition is fulfilled!\n");
printf("The if condition is not fulfilled!\n");
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From the code snippet, if x = 3, then the first printf() will be executed else the second printf() will be executed. So a simplest if form is shown below.
if (condition)
{
statement(s);
}
next_statement;
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If the condition is true, the statement(s) is executed else the next_statement is executed. Similar to the loop discussed in the previous worksheet, if there is more than one line of code, you need to use the curly braces. Let make the previous example as a full working program.
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Create a project named ifprog. Then add C++ source file named ifprogsrc to the project. Don’t forget to set your project to be compiled as C code. Then try the following C program.
#include <stdio.h>
int main(void)
{
int x;
printf("Enter an integer: \n");
// you can try using scanf() for older compilers...
scanf_s("%d", &x, 1);
if(x == 3)
{
printf("x = %d\n", x);
printf("The if condition is fulfilled!\n");
}
printf("This is the next statement, after the if body...\n");
return 0;
}
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If 3 is entered the output is shown below. The x == 3 is true then the if statement is executed.
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If other than 3 is entered, the output is shown below. The if statement is skipped because x == 3 is false. Take note about the different between = and ==.
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By expanding the simplest if statement, the if-else constructs make C/C++ more flexible in selecting options based on several conditions. For example:
#include <stdio.h>
int main(void)
{
int x;
printf("Enter an integer: \n");
scanf_s("%d", &x, 1);
if(x == 3)
{
printf("x = %d\n", x);
printf("The if condition is fulfilled!\n");
}
else
{
printf("x = %d\n", x);
printf("The if condition is not fulfilled!\n");
}
return 0;
}
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The general form is given below.
if (condition)
{
statement 1;
}
else
{
statement 2;
}
next_statement;
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Again, by expanding the if-else statement, we can build a program with any number of conditions and the respective options.
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Program input and output samples are given below.
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The general form is shown below.
if (condition1)
{
statement 1;
}
else if (condition2)
{
statement 2;
}
else if(...)
}
statement ...;
}
next_statement;
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Another variation is checking several conditions for an option. In this if construct, every if must be matched with the else. For example:
#include <stdio.h>
int main(void)
{
int year, train;
char curr_post;
printf("Are you qualified for a Manager promotion?\n");
printf("Enter the number of year: ");
scanf_s("%d", &year, 1);
printf("Enter the number of training received: ");
scanf_s("%d", &train, 1);
printf("Enter your current post(J - Junior, S - Senior, A - Asst. Manager): ");
// don't forget the space before %c else the execution will stop prematurely...
scanf_s(" %c", &curr_post);
if(year >= 10)
if(train >= 5)
if(curr_post == 'A' || 'a')
printf("Qualified to be promoted to Manager!\n");
else
{
printf("Become Assistant Manager first.\n");
printf("Need more training.\n");
printf("Need more experience.\n");
}
else
{
printf("Need more training.\n");
printf("Need more experience.\n");
}
else
printf("Need more experience.\n");
return 0;
}
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A sample input and output is shown below.
-------------------------------------------------------------------------
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In this example, to be promoted to a manager post, all the three if statements must be true.
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In Win32 Tutorial you will notice that the if statement is very useful for simple C/C++ code troubleshooting. We can test/verify/check by skipping certain line of codes to verify whether the error is generated by the skipped code.
| Main |< C & C++ while & do-while loop 2 | C & C++ if and if-else 2 >| Site Index | Download |
The C Selection if, if-else, if-else-if, break, conditional/ternary operator and switch-case-break: Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6
tenouk.com, 2007