The If Statement

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The If Statement

• ATS 315

2
if

• Used to make decisions in a program.
• Used in combination with else to create many
  possible actions in a program.

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if

• This example scans in a temperature from the user.

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n)
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if

• If the temperature is less than 0.0

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n)
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if

• then the program will run the stuff inside the
  curly braces!

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n)
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if

• In this case, that means it prints It is cold!

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n)
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if

• More complicated actions can happen with the
  else statement.

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n) else
printf (Not too bad\n)
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if

• Now if the condition is FALSE

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n) else
printf (Not too bad\n)
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if

• the program will run the code between the curly
  braces AFTER the else!

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n) else
printf (Not too bad\n)
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if

• In this case, it will print Not too bad.

main () float temp scanf (f,temp) if (
temp lt 0.) printf (It is cold!\n) else
printf (Not too bad\n)
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if is tricky, too

• Dont use use

main () int i,j scanf (d,i) scanf
(d,j) if ( ij) printf (They are the
same!\n)
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if is tricky, too

• is for assigning a value to the variable.
• is for testing a value in the variable.

main () int i,j scanf (d,i) scanf
(d,j) if ( ij) printf (They are the
same!\n)
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if is tricky, too

• In general, floats cannot be equal, so dont test
  for that.
• Rarely a problem.

main () if (potTemp 298.7) printf
(Will not happen!\n)
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if is tricky, too

• Cannot use for strings.

main () if (mystation yourstation)
printf (Same station!\n)
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if is tricky, too

• Use !strcmp(string1,string2) for strings
• Means string compare.

main () if (!strcmp(mystation,yourstation))
printf (Same station!\n)
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In Assignment 8
while(!feof(fin)) fscanf(fin,s d d d d
d,station,tempcode,) / DECODE THE
OBSERVATION / tempF ((float) tempcode
)/10.0 blah blah blah / IS THIS THE STATION
REQUESTED BY THE USER? / if (!strcmp(mystation,s
tation) /PRINT OUT THE OBS FOR THE CITY
/